I would actually suggest sending a mail to for example Audiotec Fischer with your inquiry, they would be able to forward you to a selection of quality installers in the preferred area.
Would be wrong to call it a mom and pop shop, but AF is a family owned business with forthcoming and geniune people running the company, and they're usually quick to reply
Latest interaction with them was to have our local distributor check with them on upcoming products (I was waiting for a particular amp that is in the works), and within 5 minutes they answered his mail with projected release date (it was about 6 months in the future back then).