Here is my collection of even period 3 cell oscillators. It includes almost all even periods from p60 through to p128 (only missing p114) and a fair number of higher periods. I've left out periods for which a 2 or 3 cell oscillator has already been posted (although I may have missed some redundant ones).

p60, 3 cells

`x = 2, y = 3, rule = B2cei3inq4jt5i6ci/S012ein3qry4q5an6i`

o$bo$o!

p64, 3 cells

`x = 4, y = 2, rule = B2eik3-kqy4jnw5y6c/S02ak3aj4i5i`

o2bo$bo!

p66, 3 cells

`x = 3, y = 3, rule = B2en3ceijr4kqrwy5ikq6n7c/S012i3ij4ci5ery6n`

obo2$o!

p68, 3 cells

`x = 2, y = 3, rule = B2ce3nqry4aer5eijy6c7e/S12k3eqr4iqyz5aiy6i7e`

o$bo$o!

p70, 3 cells

`x = 5, y = 1, rule = B2cen3cijkr4aeikz5ijq6aci7e8/S01c2-ck3ekqy4ckw5-aikq6ci`

obobo!

p72, 3 cells

`x = 4, y = 3, rule = B2cen3ajn4aeijknt5ay6a7c/S023ry4it5aiy6a7e`

o2bo2$bo!

p74, 3 cells

`x = 5, y = 1, rule = B2-an3ay4jkrz5jkq6i7e8/S02ae3nqy4aceiqrt5aen6aci7c8`

obobo!

p76, 3 cells

`x = 5, y = 1, rule = B2-ae3-cikn4aceknty5cy6ck7e/S13n4w5cj6ci8`

obobo!

p78, 3 cells

`x = 5, y = 1, rule = B2cik3a4ac5ai6c8/S02in3jn4ai5enqy7e`

obobo!

p80, 3 cells

`x = 4, y = 2, rule = B2-an4eit6k/S1e2aek3ry`

o2bo$bo!

p82, 3 cells

`x = 4, y = 1, rule = B2cek3ckny4eiqt5-ikry8/S02en3iqry4inr5cy6c`

2obo!

p84, 3 cells

`x = 2, y = 3, rule = B2-ae3aejr5jq7c/S01e2-ck3cei4artw5cein6k7c`

2o2$bo!

p86, 3 cells

`x = 5, y = 1, rule = B2ci3ajkn4cejnrt5knq6ik/S02i3inqr4ceik5c6ci`

obobo!

p88, 3 cells

`x = 5, y = 1, rule = B2ce3cekr4ckt5ny6i8/S02aen3aciky4jknry5i6i`

obobo!

p90, 3 cells

`x = 5, y = 1, rule = B2cn3ainqy4eijkt5ny/S02-ac3jry4cejnt5e6ci8`

obobo!

p92, 3 cells

`x = 5, y = 1, rule = B2cei3ijk4ce5i6ai/S1e2ai3jny4e5ey`

obobo!

p94, 3 cells

`x = 2, y = 3, rule = B2cek3iy4iq5aci/S01c4a5k6c`

o$bo$o!

p96, 3 cells

`x = 4, y = 2, rule = B2-ac3aeijn4n5a/S03ijk4qwz`

o2bo$bo!

p98, 3 cells

`x = 3, y = 3, rule = B2-ac3acik4cenqt5ijnqy6e7c8/S02ack3ceky4-iknyz5aejq6c7e`

obo2$o!

p102, 3 cells

`x = 2, y = 3, rule = B2cen3-cikn4acijr5cinr6ck/S1e3ai5i`

o$bo$o!

p104, 3 cells

`x = 5, y = 1, rule = B2cin3ajnr4ijqt5ejnry6a8/S02a3-jnry4inrty5eny6ek`

obobo!

p106, 3 cells

`x = 3, y = 3, rule = B2-ae3-knqy4ijky5aejnq/S02ei3aein4cijqrw5ai`

o$2bo$o!

p110, 3 cells

`x = 5, y = 1, rule = B2cik3aciky4-ejqz5aq6c/S1e2an3cy4acn5r6k`

obobo!

p112, 3 cells

`x = 2, y = 3, rule = B2-ak3jqy4wy5acer6i/S01c2en3-cq4jqrtwy5ky`

o$bo$o!

p116, 3 cells

`x = 3, y = 3, rule = B2-ae3aejy4knqrz5cek6aik8/S01c2cn3jq4qwy5kn6c`

obo2$o!

p118, 3 cells

`x = 3, y = 3, rule = B2ein3cijkr4jknrtyz5-ceir6-ai7c8/S01c2acn3cejy4-cijny5ay6-ce7`

obo2$o!

p120, 3 cells

`x = 5, y = 2, rule = B2cin3-jknq4ekrtwy5ainr6ik7e8/S02cen3-aknq4acrw5iqry6e`

obo$4bo!

p122, 3 cells

`x = 4, y = 2, rule = B2-ae3acnr4nqr5-ceky6ckn7/S1c2aei3q4ajkqr5-qry6-a`

o2bo$bo!

p124, 3 cells

`x = 5, y = 1, rule = B2-a3ijy4ekyz5ac6an7c8/S1e2in3ceqr4acejqw5acr6ack7e8`

obobo!

p126, 3 cells

`x = 5, y = 1, rule = B2-a3aeqry4kqt5-acir6eik78/S02eik3eijnr4-eikqt5ir6aek8`

obobo!

p128, 3 cells

`x = 4, y = 2, rule = B2eik3ijqr4knqrtz5ijkn6-ci7e/S02aei3cijqy4aknq5c6e`

o2bo$bo!

p136, 3 cells

`x = 2, y = 3, rule = B2-ak3ac4ejkr5airy6ce7c/S12ain3knq4nqr5cijr6i7e`

o$bo$o!

p138, 3 cells

`x = 5, y = 1, rule = B2-ai4ijnw5aceq6ek/S01c2in3inqr4-erwy5eikqy6c7`

obobo!

p140, 3 cells

`x = 5, y = 1, rule = B2-ai3cjky4iknrtwz5-nry6ci8/S02kn3iqy4-ijnt6k8`

obobo!

p142, 3 cells

`x = 3, y = 3, rule = B2cen3aqr4arw5ijknr6cn7c/S01c2ae3-aeiy4cejnqz5ckry6acn`

obo2$o!

p144, 3 cells

`x = 4, y = 2, rule = B2-an3ajky4ainqt5-aeny6ck/S02ck3ekry4aijkrz5inr6ak7e`

o2bo$bo!

p146, 3 cells

`x = 5, y = 1, rule = B2-ak3cejry4aknwyz5cejkq6e7e8/S12n3jk4ijrz5jr6ei7e8`

obobo!

p148, 3 cells

`x = 2, y = 3, rule = B2-ak3inqy4acjqrtz5aekry6k7c/S01c3kq5y7e`

o$bo$o!

p150, 3 cells

`x = 5, y = 1, rule = B2-ak3cijr4aektz5ci6-in7/S1e2eik3ckq4w5acy6n8`

obobo!

p152, 3 cells

`x = 5, y = 1, rule = B2cik3aekn4jqtz5aen6n7/S02-ce3-in4jkty5-anr6cei`

obobo!

p156, 3 cells

`x = 3, y = 3, rule = B2-ae3aejqy4cjwz5-akn6akn7/S02ai3cekry4acjktwy5ceiq6aek78`

obo2$o!

p158, 3 cells

`x = 2, y = 3, rule = B2-ak3-ckqr4eiknqt5cny6ce7e/S1c2i3e4ej5y6a`

o$bo$o!

p160, 3 cells

`x = 5, y = 1, rule = B2cik3-cnqy4-aejqz5acij6ce/S02n4-qrwyz5qy6-in7c`

obobo!

p162, 3 cells

`x = 2, y = 3, rule = B2-ai3nr4jkt5jry/S12ace3cknr4qz5eijry6i`

o$bo$o!

p164, 3 cells

`x = 5, y = 1, rule = B2cek3ajkr4ikrwyz5eq6-an8/S02k3kr4eiknw5n6ci8`

obobo!

p168, 3 cells

`x = 3, y = 3, rule = B2-ai3enqy4aiqt5iknr6cek7/S02-cn3enqr4iqz5cqr7`

obo2$o!

p170, 3 cells

`x = 5, y = 1, rule = B2-ak3-acny4arz5-cijn6-cn7/S1e2ik3jnqry4ceijkt5ay6-ai7e`

obobo!

p180, 3 cells

`x = 5, y = 2, rule = B2cek3ciky4anqr5cknr7c/S01c2ckn3eiry4ajryz5ekry6ae`

obo$4bo!

p182, 3 cells

`x = 5, y = 1, rule = B2cin3-jr4knry5-cjry6aei/S02ai3ijkqy4acjnr5einr6ik`

obobo!

p188, 3 cells

`x = 2, y = 3, rule = B2cei3ir4cekwy5aeq6a/S12k3ij4ejy5ciry6ei`

o$bo$o!

p190, 3 cells

`x = 2, y = 3, rule = B2cei3ciq4ajnqz5ejk6ck7e/S01c2-ek3q4rwy5aek6c`

o$bo$o!

p214, 3 cells

`x = 5, y = 1, rule = B2cik3ajqy4cjkqrwz5aceq6ak7c/S12ck3aijqr4cqwyz5-cqry6-c7c`

obobo!

p216, 3 cells

`x = 5, y = 1, rule = B2ci3aeinq4ejqrtz5-ijy6aci/S02en3ceinr4ajny5aeiny78`

obobo!

p224, 3 cells

`x = 5, y = 2, rule = B2-ae3aejr4ajkntyz5kq6a7e8/S01c2i3jqr4acijrwz5ceikn6ik7c`

obo$4bo!

p232, 3 cells

`x = 5, y = 1, rule = B2cin3-cknr4aejqyz6eik/S01e2a3ijnr4jqr5r6c8`

obobo!

p234, 3 cells

`x = 5, y = 1, rule = B2-ai3ry4-ajkwz5-aekq6a/S01e3ar4aciwy5cejn6i7c8`

obobo!

p274, 3 cells

`x = 5, y = 1, rule = B2cik3-ejn4-rty5-aejk6-ck8/S1e2n3kn4aw5cny`

obobo!

p304, 3 cells

`x = 2, y = 3, rule = B2cek3ekny4aejnwz5-cjqr6k7c8/S12-ac3iqy4z5ein6ce7e`

2o2$bo!

p314, 3 cells

`x = 5, y = 1, rule = B2ikn3-jqry4ceitwz5-cej6ikn78/S01e2en3ain4et5eijky6kn7e`

obobo!

p344, 3 cells

`x = 5, y = 1, rule = B2eik3ij4ciqtyz5iy6e7e/S01c2ckn3-ikqr4enz5acikr6ci8`

obobo!

p358, 3 cells

`x = 5, y = 1, rule = B2cin3-ejry4einrwz5ijk6aci7c/S1e2k3ik4cikryz5i6ci`

obobo!

p368, 3 cells

`x = 2, y = 3, rule = B2ce3iny4aeinqw5acr6-ci7c/S12e3knr4acjrt5ai6e`

2o2$bo!

p376, 3 cells

`x = 5, y = 1, rule = B2-a3aqry4ejnry5ceinr6-kn7/S01c2cin3aijky4ajnqz5cknqr6-en7`

obobo!