Depends on the game, what are you trying to fix? I've heard of them for Trons and Atari System 1's. I rebuilt a Sega Turbo but I had to chase down the parts myself.
Bob Roberts has cap kits for some of the old linear power supplies. If you are looking to rebuild a modern switching power supply Ken Layton has written a few guides on replacing failed components. They are hosted by Mike Roma.
i have 2 MCR's... ( think that's what ya call them )... for rootbeer tapper and such. 1 for a stern/seeburg for my Amidar and 1 for my new Gorf project.
pretty sure Bob sells rebuild kits for the tapper and gorf. Never looked into one for a stern. Although I know they can be replaced with a switcher and work fine. Probably doesn't help though.