Originally Posted by True Faith
Sorry, that wasn't clear in my post--I tried the tire dealers on the Maxxis website in my area; they are the ones that said they could not get the tire. I also tried Discount Tire Online, which sells some Maxxis tires, but they said that they do not stock the compact spares.
Ultimately, I did e-mail Brad, who indicated that the easiest way to source the tire is to go through a car dealer (he said any GM dealer would be able to do it). Separately, I'd contacted Lindsay Cadillac in Alexandria, VA, who apparently had also contacted Brad; they were able to order the tire for me from Maxxis. It should be here in 3-5 days, with a total cost of less than $100.
To sum up, you should be able to get any GM dealer to order the Maxxis tire for you, but if you are having trouble try Lindsay Cadillac.
Tire came in and was mounted yesterday. Looks a lot nicer and fits a lot better than the T125. I'm glad I went to the trouble of ordering the Maxxis, and thanks again to Greg for figuring all of this out.
Here's a slightly better shot of the spare in the trunk of an E90.