I've taken mine to Prestige Imports and they've done a good job. Dealer, not indy though.
For more performance oriented stuff, I've also taken it to 3R Racing, I imagine they would do regular maintenance too.
Our local Porsche Club region (Rocky Mountain Region) is full of VERY knowledgeable (and nice) people. I know they have a Facebook group page where I bet someone could give a better answer.