From article linked on their main page, the GOA seem to support Hunter, Huckabee and Ron Paul.
http://gunowners.org/pres08/powder.htm
I think you already know two I’d remove from that list, but interesting reading on Second Amendment issues on all Republican (and DUocrat) candidates on the main page:
http://gunowners.org/pres08/index.html
All three are good on the 2A. But I’ll take the guy who used a firearm in combat, myself.