Hi Shelley and Sean
I've been doing a lot of investigation on the compact spare for the SC430. I discovered that the 2004 Acura TL with the Dynamic Package uses the identical compact spare tire and wheel, namely the T145/70R17, as the SC 430. I was at the local Acura dealer and they had the wheel company on the phone and the wheel company confirmed that the wheel bolt pattern is identical for both cars.
The price that i was quoted was $500 (Canadian), as opposed to the $1,000 (Canadian) from the Lexus dealer. Keep in mind that the Lexus price included a floor mat trimmed to fit around the spare, a bolt to hold it in place, and a cover for the spare.
Check it out and let me know if my infomation is correct.
Arnie