I would personally do the defender/stargaze layout since most of the other games only use 2 or less buttons so you could just use the two main defender buttons and it would still be normal. I find it hard to play defender or stargaze with all 6 buttons in a rectangle but that's just me.
No I'm not sure which roms are the rainbow edition ones, sorry. And i would check KLOV to see if anyone has them and you could post a wanted ad to if you wanted to. Someone there would probably have the whole pcb if you couldn't find the roms you're looking for.