Boy just provided me this location and link, i haven't been there yet but he bought a biker jacket for his girlfriend and was very satisfied. According to him, a family run business, husband runs this shop and wife the one most of us know at the Sailomjoy market near the border. Cannot verify if that one is still open as when David and me went there last time some months ago, it was closed up.
maps.app.goo.gl
Jcf biker shop · Mae Sai District, Chiang Rai
maps.app.goo.gl