I have a serial Memory Stick (up to 128 MB) reader lying around somewhere. Came with my camcorder back in 1999. (The digital still camera bought at the same time came with one of the 'FlashPath' floppy adapters.)

Won't help you with your SD card, but if you just want to be able to get a flash memory card working on a 68k desktop Mac, it's probably your best bet.