I can't remember how I won AM the first time around, but in my 2nd game, I have 60 bases and have seen no new ships in a very long time nor have I had the opportunity to capture new bases.

I've the Retribution researched but need to research an interplanetary ship to build a ship for the endgame.

Any ideas?

Are you aboslutely sure that you've researched everything available for research? I haven't finished the game yet so I can't tell you, but often I've read these forums wondering what weapons ppl were talking about, only to notice that I hadn't research something that lead to the possibility to research the mystery weapon in question.

The trouble I had is that I had a fairly long wait gfor the interplanetary vessel to land after I'd researched the Retribution. I think I managed to watch two months go by (in-game - I'm not that patient) before it landed and was available as a mission. I practically had to set all my outer bases to anti-biomass just to keep my territories safe, leaving me with very few manufacturing bases or research bases

It should turn up soon, not that that's much help to you