I don't have any direct experience with any shops' repair services past when Impact Airsoft was around, as I worked there as a tech for a decent amount of the time it was open.
Read and understand the above statement, and don't take the statement below to be fact by any means.
I have heard (heard) nothing but relative horror stories from other places on their tech services. A story including one of the local places having destroyed a set of Siegetek gears somehow. Missing and stolen parts while guns were in for repair.
Places that I (myself) know will take on projects and offer tech services, are Phoenix Tactical and Eastside Commandos. I'm sure those arent the only places around that do. But stores aren't the only places to get projects worked on.
There are a number of private/individual techs in the state and local area. A few of which include myself, Deacon, and more.