Original Cisco 2GB Compact Flash CF card,Memor card | eBay
Amazon.com: Cisco 2921 Integrated Services Router - 1 x SFP (Mini-GBIC), 2 x CompactFlash (CF) Card, 4 x HWIC, 2 x Services Module, 3 x PVDM - 3 x 10/100/1000Base-T WAN - CISCO2921-SEC/K9 : Electronics
Installing and Replacing CompactFlash Memory Cards - Cisco