Check out pangeareptile.com for a good rhac specific forum, products, and care sheets.
Here's their garg care sheet:
http://www.pangeareptile.com/gargoylecare.htm
Gargs and cresties are kept pretty much identically.
Two of the most well known people in Rhac breeding are Phillipe de Vosjoli (spelled right?) and Allen Repashy. Along with Frank Fast, they wrote a book together which is top notch and I recommend though it is pricey at around $40.
For gargs I'd certainly look at lots of other breeders as they are very numerous in captivity. You can find them at just about any reptile expo, they are slightly less popular than crested geckos but if you find cresties, you should find gargs. I recently picked up one from a show in Iowa!