I built some from scratch, it wasn't too hard. Your best bet is to probably get reference of GB2 packs and just come upon random items that are the right shape and size for the complex parts and build it mostly out of styrene, for example (this is no high tech, super accurate thing...) I used some small clothing buttons as the... cyclotron? I think it's called. It worked at the time. The back was made of styrene, with plastic tubing details and guitar wire to act as the ribbed tubing.