There are a number of custom ROMs out there that are not carrier specific, I'd personally recommend OMJ's Manila 2D v3... even though it's getting outdated (since he's got a Diamond now, and not currently working on ROMs)
If you want a carrier specific one, you might try rstoyguy's USCC ROM... I'm not sure how similar it is to the official ones (ROMs) you guys got... I would assume it's got GPS working..
http://forum.ppcgeeks.com/showthread.php?t=36763