I have been give this information of a Paintshop in Lampang. I have no personal Experience but high recommendations!
The particulars for Billion Colour body shop are;
Owner, K. Toe (something like that)
Address, Thanon Boonyawat near Phahon Yothin Rd. (Alt. Rt. 1)
Tele, 086 673 4004
Coordinates, 18* 17.460 N, 99* 30.502 E
The easiest way to find it if you are coming from Chiang Mai is to take Hwy 11 to Highway #1 and turn left towards Chiang Rai. Go all the way to the Rt 11 junction and turn LEFT back into the city. At the first traffic light (Phanon Yothin Rd.) turn left again. Turn right at the first intersection (Esso Station on the corner), go past the Esso Station and make a right turn into the body shop driveway.
Good Luck.