Two seasons ago I needed to have a set of new full-tread RA1s shaved and did a lot of looking around the area. I didn't find much. I asked Lee one day at the track and he said he had a tire shaver, but it was in storage and it had been a loooong time since he did any shaving. He was reluctant to get it out. Maybe you'll have better luck.
What I did find was a guy, like the ONLY guy still in Michigan, that shaves them in Mason for a lot of dirt and circle track racers. The shop's name is Roger's Cline Tire http://local.wilx.com/roger+s+cline+tire.9.54354970p.home.html
. The shaver's name is Neal. I had him do a second set last year, maybe call them and see if he is still there. It was $20 a tire and he'll do it to any depth and angle you want. It really is a lost art. Not that you need anymore info on it, but I wrote an article on it after my first experience. http://blog.caranddriver.com/the-lost-art-of-tire-shaving/