The only
GW event in the US is Game's Day, but the support for the event is in a decline in most places. Last year, the US Game's Day was held in Tennessee (where their US headquarters is located) and from everything I read, it was much more low key than previous years. Your best bet is to go to other cons and enter painting competitions there. One thing to keep an eye out for is any kind of
Crystal Brush qualifier.
AdeptiCon, which is held in Chicago, just finished up a week or so ago and is probably the most popular gaming cons in the US and is also where the Crystal Brush finals are held. Lots of other cons that run painting competitions offer Crystal Brush qualifiers, such as the Las Vegas Open and TempleCon.
You location says you live in Virginia, so you are also in luck because Virginia hosts the
NOVA Open in Arlington and it has been growing pretty quickly. It's held at the end of August and they run a painting competition called the Capital Palette.
You can also check any local shops, but
GW and independent, to see if they are running any competitions. If not, talk to the owner(s) and see if they can start one up. It's usually a pretty good way to get your feet wet.