I'm loving Chandler Air Service (
www.aerobatics.com). They have a nice sized fleet, everyone is really nice, and the price is decent.
I haven't had any problems with aircraft or instructor availability.
I also looked into Falcon Executive Aviation, and it seemed like a decent place to go also. The reason I didn't choose there was because it wasn't as "family-like" as I hoped, and the airport is really busy. The instructor I talked to said that they have an average 30 minute wait at 6:30am in the run up area!
On the western side of Phoenix, there is Glendale Aviation, which I looked into and was told that they would have trouble fitting me in because of lack of instructors. That was a few months ago though, so things may have changed.
I'm not sure what's all available at Deer Valley, Gateway, Steller, or any of the other airports here. I also have no info on academies like ATP or Pan Am, Sabena, etc.
Drop me a PM if you have any questions!