J.P.
You can try Angies List, but they have a fee. You can also ask any home inspector, but check them out too. All states have different laws about home inspectors and some do not know what they are doing.
I would Google radon testing in your area, check out what companies come up and read any reviews.
This one came up with 21 Google reviews and a Super Service Award from Angie’s list.
http://www.structuretech1.com/