What is offered after Course III? I've heard of a "Masters" class -- is that something that is offered the same way as the I-III classes?

Wilton has courses offered right at their location.
Here's the link for what they have:
http://www.wilton.com/classes/wiltonschool/classes.cfm
Also try local bakeries to see what they may offer.

My local cake store offers all kinds of specialty classes. Fondant and gum paste, petits fours, dobage, candy, brushed embroidery, cookie arrangements......and so on. They are a lot of fun. Ms. Fran one of our local Wilton instructors is GREAT!!!!!

Cake Art here in Atlanta has a course 4 and then they have specialized classes in gumpaste, rolled fondant/buttercream, wedding cakes, etc.

Nicolas Lodge also has classes and he travels across the country. I have seen a listing of his classes and they are upwards of 300.00!!! Since I am a newbie, I don't see the need right now. Maybe eventually.