Replacement Onstar Antenna Mast

HELP! The external Onstar Antenna mast on my '02 Intrgiue cracked in half and I'm having a tough time trying to find a replacement. And suggestions or pointers to finding a replacement mast are very appreciated. BTW: I tried the local GM dealer but for $51 bucks I'd have to buy the entire assembly including the piece that mounts to the rear window. I don't need that - just the mast.

Thanks in advance for your help,
Mike