VO is what I used for alot of the generic SFXs like boosting, inflight, transformation and missile launching.
Now for walking and mechanical movements, those are a bit hard to find in my opinion....I'm into fandubbing and audio mixing so I gotta sometimes find a episode of something where I can just get a second or two of some specific sound and rip it....
Another idea, get a video game, mute the music, put it on 2 player and just use that while recording. I need to borrow a really good mic from a friend to get the best clear sound as possible.
But like Gundam games and even DYRL for the PS1 works just as well, those are all original SFX.