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The tire pressure monitors on the 05 will not work on any C5 at all, you'll need your original units in there. The 05 wheels themselves will fit on a C5, but you should run spacers on the back wheels for an exact fit (although some people don't bother, it's only a small spacer that's needed)
I doubt those places will have them in stock but they can probably order them for you. I've seen them in Jegs and Summit catalogs and both those places usually ship same or next day. I've also seen them on at least one of the Forum Sponsors. It may have been Southern Car Parts and I know CCW wheels has them.
you don't need the spacers. It only looks like wheels will rub with the car in the air and tires off the ground. Once the car and tires are in their normal sitting position you have probably 3/4" clearance. I have run mine with and without spacers and currently run with no spacers. I do not rub and my car is lowered. You will be fine.