I know someone to avoid: Maryland Offshore Performance in Rockville. They quoted me $506 to replace the reverse shift cable, and I provided the part! Took me 2 hours to change it myself, including a trip to the hardware store, and it was the first thing I've ever done to the boat. Now I work on the boat myself.
There are some guys that advertise on Craigslist that they will work on Sea Doos. Northern VA has a BRP dealer, Coleman Powersports. I haven't been there, but they were helpful with parts when I called.