I've bought a few trees from Bob and Todd and I've been happy with them. They've all been healthy, and Bob and Todd are very helpful.
Another good source is the PBA convention in the spring. There are quite a few vendors that come in, and there are a lot of trees for sale. I would suggest going Friday if you can, the good material seems to go early.
Unfortunately there isn't much out in C'ville. You're going to have to drive a bit.
Gardens Unlimited in Ladysmith (actually Ruther Glen, but Ladysmith is the exit off of 95 you take to get there) is arguably the best bonsai nursery near D.C. and Richmond, possibly up to Philly and down to Raleigh.
I've posted in the past about the place. Here's a link to the Rappahannock Bonsai club. Bob and Todd are the founders. The photos on the blog are of Gardens Unlimited: http://www.rappahannockbonsaisociety.com/
They are a tad pricey. But all their trees are excellent. I've been doing bonsai in N. Va. for almost 20 years and have been to most of the bonsai nurseries within 4 hours of here. This one's the best in the Middle Atlantic, IMO.
To the north, Chase Rosade at Rosade Bonsai just North of Philadeliphia in Bucks County is another standout. http://www.rosadebonsai.com/
Chase has been doing bonsai for almost 40 years now--possibly longer. He is very very good. The National Arboretum has a few of his trees on display. The nearby river town of New Hope, Pa. is a great place to visit (and keep the spouse entertained) while you look at trees
If you're in DC I would stop at the National Arboretum to see the National Bonsai & Penjing Museum. It's not a nursery and does not sell anything, but they literally have hundreds of world class bonsai and it's a magical place to be. The architecture and landscape architecture is amazing. You will get plenty of inspiration there...
Check out the link and browse around. The best one I saw was a Japanese white pine that started training in 1625...