my friend has an unknown brand alarm installed in his GSR, but his alarm remote is crapping out on him. what options does he have as far as replacement? does it have to come from the same manufacturer as the alarm itself?

 

Yes, it needs to come from the same manufacturer.

You need to determine the make/model of the alarm (done by physically looking at the brain) and then contacting the appropriate company. If said company is Bulldog or Chapman, or just doesn't have a name on it, pull that **** out and buy something reputable like a DEI (Viper/Clifford/Etc) or Compustar.