I just bought the Nintendo NDSL 100 for $9.99 in KMart/Sears here in the US. It was perfect for what I wanted to do with it. It essentially looks like a camera pouch but is tall enough to fit the whole thing in. It has two outer pockets, one for pens and the outermost just big enough to fit in the i-Blue 737 GPS unit. The flap fits over it and snaps into place near the bottom. It has a detachable neckstrap and a carabiner that can be attached to a belt loop. If I slip in the n800 button side in first, the unit can be in sleep mode and not be triggered by jostling. I also found that hte gps could still see satellites through the material (and this was inside a house). It's hard to find a decent picture of it but I found a good one on a German site:
http://www.wolfsoft.de/shop/product_...ndsl-100).html

It comes in several colors.