Most tint shops buy direct from the manufacturers, but here is a wholeseller that seems to have good prices...

http://www.tintwholesale.com/

Tinting is one of the most simple things to do. However, it is very hard to do it right. Out of the Tint shops, I only know a few that actually do a great job. A lot of shops allow up to 5% flaws in the job because they know they do not do the best job and don't want to be redoing it several times. So my advice is to really work on your skill because the quality is what going to set you apart from the others.