I think this micro drive will work on 6502 based products. It is 5 volt and its slow speed is 300 bps (they used the word "baud" which is commonly used wrongly).
“Most micro-controllers have small and limited on-chip memory. For those applications that require large volumes of data, the uSD-G1 with the GOLDELOX-DOS chip is a simple solution in a form of a tiny ‘drop-in- module’. A simple serial interface is all that is required to take away the burden of low level design that would otherwise be required for the host controller. The micro-DRIVE module utilises common microSD memory cards of up to 2GB of capacity as its medium. A handful of straightforward commands provide direct access to the onboard memory card or storing and retrieving any size or type of data. Access to the card can be at (FAT based)"
http://www.sos.sk/a_info/resource/c/4Ds ... S-rev2.pdf