http://www.platatac.com/plat-a-tac-m...v/w1/i1002035/
I have one of these that I transfer between a few rigs. It attaches with the Velcro strap so you won't loose it if you drop it, yo can fit a field map plus radio freqs and other notes inside for handy reference. You'll see them on eBay cheap.
If you know someone who sews they could turn one out pretty easily. It's just a giant envelope.