Check with your local extension office. I'm sure they hold Master Gardener classes but you'd need to be willing to give back some volunteer time to be qualified for them. Many of the extensions offer classes for the public, too. They should know if there are any horticultural gardens or nurseries that provide classes. If you can come to Richmond, Lewis Ginter Botanical Garden has many classes every year. Here are a couple of links for you:

Extension offices in VA
http://www.ext.vt.edu/offices/

Lewis Ginter
http://www.lewisginter.org/

Sandy

Although it sounds as if you are looking for something more advanced, many of the nurseries in northern Virginia offer seminars/classes frequently. I have been to several at Merrifield gardens and I know Campbell and Ferrara and Behnke's have classes as well. Green Spring Gardens in Alexandria is another resource-their folks are very knowledgeable. Good luck. Cynthia