Here is a list of Porches independent mechanics.
I often suggest you pick your mechanic before you pick the car. And then ask them to find a car for you that they are familiar with.
I drove a TIP 986 for probably 5 years daily in the DC area. Bought two, found a motivated seller and negotiated hard. Did a PPI on the second one. Wise move. Fixed what was needed and almost zero trouble after that.
Dealers are often reluctant to allow another mechanic to work on cars they own. Private sellers less so if they are convinced you are a serious buyer and have already negotiated a price contingent on the inspection results.
I just popped into craigslist and am amazed at how few Boxsters are for sale in the DC listings. Very few 987 models. Great driving weather immediately ahead. And there is a major major change coming the end of the year that may have more people holding on to their 6-cylinder Porsches to see if they appreciate.