You shouldn't hold your breath while waiting for Raven to release more map sources. They have ceased their live developer support to these games, and apparently archived their files, according to the info I got from them, when I asked for something (not a map source but something more useful, reasonable and sensible).
One problem might be that as a company, probably some lawyer has to be contacted before they can release anything really useful. This is of course all my speculation, but somehow it needs to be reasoned why things are so hard...
And besides, getting a map source and editing and then releasing it under your name are two totally different things. And to be honest, if you don't know how to map in the first place, I don't really see how you could make an existing professional map any better, anyway.
Frozen by ICARUS