What is the Flash on these cards? Is the flash chip distinct from the main controller chip? If so, is it a tiny little serial flash (eight pin SOIC) or is it a larger parallel flash chip? What are the markings on the cards with too small capacity? On the stock card where it works?

Get me that info and I bet I can find a replacement flash easily enough. That might not be enough to make it work, but it might and if it is a serial flash, those things really aren't that hard to remove and replace.