Search around on eBay and you're bound to find PCMCIA type 1 spec memory cards in sizes larger than that of the standard Neo-Geo memory card. Here is a scan of one such card I picked up via eBay:
Happy hunting!
Edit: fixed image link
[This message has been edited by DolphinLord (edited September 28, 2000).]
Yeah, they usually go for next to nothing. I think I paid around $15 total for mine. They're old tech, and almost no one wants old PCMCIA memory cards of such low capacitance.