While it's a GBA clone instead of the original Game Boy, there's the K1 GBA that can play original carts and has a cartridge that will accept a microSD for roms

While it's a GBA clone instead of the original Game Boy, there's the K1 GBA that can play original carts and has a cartridge that will accept a microSD for roms. I was really interested in them a couple of years ago but then I found emulators for my PSP.