You should be able to use the antenna from most of the larger body GM cars (Park Ave, leSabre, Bonneville, Olds 98 olds 88, and maybe some of the w-bodies)
To replace it, you need a 10mm socket. You undo one mounting bolt, and the ground wire I believe (might be a second mounting bolt, but they are easy to find) With them removed, you undo the connector with the wires coming from the radio, and the antenna wire. Then you pull the antenna down, and pull the drain tube up. To replace, reverse the steps.
You might have to remove the jack box first, which I believe is 3 10mm or 8mm bolts, then the carpet can be removed.
There are some differences in the antenna masts, but they don't affect functionality.
2007 Saturn Aura XR | 1970 Chevy Blazer 4x4 | 1970 GMC 3/4 Suburban 4x4