Quite some time ago RBSC has published the project of the MultiMapper Cartridge 1.0 with 512kb FlashROM:
https://github.com/RBSC/MultiMapperCartridge
We don't sell assembled cartrdidges except for Carnivore2, but some people were asking us to sell the MultiMapper cartridges. A few people even tried to assemble those MultiMapper cartridges on their own and experienced difficulties in getting properly working CPLD or FlashROM chips. Besides, soldering those chips is not trivial and not everyone can do this. But it seems that one of Chinese companies is now making and selling our cartridges on AliExpress. We did not give them the permission to produce those cartridges, so this is unauthorized version:
https://aliexpress.com/item/1005004754219281.html
But if they work fine - we have no objections against people buying those cartridges. But be warned - the we didn't check the quality of the production, so we won't support those unauthorized cartridges.