Dunno off-hand myself, but I bet this site would be a solid start:

http://az.pca.org/

-or better still-

http://forums.rennlist.com/

By performing a cursory search, this last one turned up the following:

"Stuttgartt Southwest and Don Jacksons are a few of more popular repair
shops. Stuttgart is probably closest it is near University and
McClintock in Tempe. Probably 10 min drive from 44th and Thomas. These
two shops can do just about the "tuning" you need short of turbo
conversion or supercharging.

Heard mixed review from Exotic,
Becks I have heard is expensive and more into aircooled stuff,
Evolution is into the newer cars, (boxster, 996, 997),
Powerhaus can build you a 560 hp 968 Turbo if you want to and have  $$$$$$$
Sun Valley, I have heard of them, not very much about them. They don't
seem to be intro the Porsche club scene."

----

There was more, but you know where, now.

Regards,

DS
95 993 Coupe