The gps feature for onstar not working

My sierra is a 07 newer body style if it makes any difference, anyway I'm trying to find out where I can find the gps module for onstar as they're not able to find/track the vehicle if I were in an accident or if it was stolen. I'm wanting to do this on my own as I have no faith in my local GM dealership because they can't give me a price for this module or how long it will take for the labour costs etc. Onstar tells me its a gm thing they have to give you the price and gm says its Onstar who has too. So ant help is appreciated