I found a bunch of cheap mini-SD sockets on eBay. Easy to solder/etc, and you can use micro-SD cards with them via an adapter. (micro-SD cards are just TOO tiny.)
(This is a mini-SD adapter for The Mattel "JuiceBox" multimedia player. At one time, these small ARM/linux-based toys were being liquidated for about $10 each. With no modifications, they'll play some pictures and MP3 files from an SD card. With "some" modifications, they can be a tiny linux system.)