The majority of the sponsors are Japanese in nature: (Cusco, Advan, Calsonic, Wedsport, Takata, Endless, SuperAutobacs, etc.) and the occasional European sponsors: (Motul, BP Oils, etc.). You'll also find that there is the occasional European driver and cars that compete: (McLaren F1, Ferrari, and Porsche) and a Dodge Viper for good measure!
There is talk that one Round of JGTC will come to the US, specifically in California. I am keeping my fingers crossed 'cause I am so there when that happens for the 2004 season.