According to the tech I talked to at Magnuson, it's the same oil for the M90 and M62. He said there's no problem at all with using the GM S/C oil in my TRD S/C.

One vehicle that I know came stock with the M90 is the '97-'03 Pontiac Grand Prix GTP. I've heard a rumor that the '03 Grand Am GT has the M62 as an option, but I don't know any more than that. I think the XTerra also uses the M62, but they don't have any S/C oil discussions on one of their larger forums.

The GM bottle of supercharger oil is not specific for a particular vehicle. It's part # 12345982. It costs $5-6 per 4 oz bottle. Yes, Pontiac dealerships should have it in stock and you should be able to just say you'd like a bottle of supercharger oil without specifying a vehicle. If you can't find it anywhere, you can buy it for $7.50 plus shipping from:
ZZ Performance

Based on what's been previously posted at a popular Grand Prix forum (www.gp-owners.com), the S/C oil is a different animal from just synthetic motor oil. The S/C oil has foaming agents while motor oil has anti-foaming agents. And some people say motor oil ate through their S/C seals after they tried it for a while. So I'd stick with the real S/C oil.

The hard part is finding something to suction out the old oil (Windex pump head, orthodontic syringe...)