A friend of mine is going there in June and I know he has some JPG topo maps, ranging from 1:250,000 down to 1:50,000. He's using Fugawi Global Nav. software on a netbook-size laptop, with a GPS puck connected by USB. Fugawi allows him to calibrate the map (pretty much any image, in fact), by putting in a few known lat/long points.
I'll ask him where he got them, if it sounds of interest? They look scanned. Unlikely to be of use with the Garmin directly, though.