Best Buy: SanDisk 512MB microSD/ TransFlash Memory Card SDSDQ-510-A10M
Amazon.com: Lerdisk Factory Wholesale 6-Pack Micro SD Card 512MB in Bulk Small Capacity Produced by 3C Group Authorized Licencee for Small Files Only, NOT Suitable for Camera or Phone (NOT GB, 1024MB=1GB) :
512MB micro SD Memory Card : ID 5252 : $4.95 : Adafruit Industries, Unique & fun DIY electronics and kits
Amazon.com: SanDisk 512MB SD Secure Digital Memory Card : Electronics
SDSDG-512-A17 SanDisk 512MB SD Flash Memory Card
Sony 512MB Memory Stick Micro (M2) Card - Walmart.com