FWIW, the links you gave for Green Thumb and Driftwood are pretty overpriced for what's being offered, IMO. Those tridents are just big telephone poles with leaves. Not much going other than diameter...those black pines are just subpar...
All this depends on what you're looking for. You looking for collected trees, or more traditional species?
Collected trees come in larger sizes for less $$ compared to more traditional species, like black pine and stewartia (and BTW, really sizeable Stewartia --4+ inches in diameter--aren't all that common and can be a lot more than $500 for a good one).
If you want collected stock Zach Smith at
Bonsai South is excellent and sells medium to huge bald cypress (in-season--he sells out quickly). He can also source other larger trees if you talk to him.
Jim Doyle at
Nature's Way has already been mentioned. I have driven up there a few times from N. Va. It's worth the trip. He has extremely nice stock and trees--sometimes has some awesome collected western conifers.
Chase Rosade is another great bonsai place in New Hope, PA. Chase is getting on in years, but his nursery is a vibrant place with A LOT of trees and pots. Bob Mahler, one of Chase's students also has a relatively new bonsai nursery (called Kifu Bonsai) near New Hope in East Greenville, PA.
If you're set on online or catalog ordering you might inquire at some California nurseries as well. I know a few folks who have sourced excellent Stewartia, black pine and seiju elm from out there
Bonchi Bonsai / Matthew Walker - Matthew sells bonsai and bonsai supplies including copper wire. He teaches classes and leads workshops. Garden open by
bonsaitonight.com
Also local clubs have auctions where spending $500 will probably get you a $1000 tree. It's worth checking websites and joining Facebook sites for clubs in Richmond, as well as N. Va. The Potomac Bonsai Association joint auction was last month, I think. It's traditionally up in Beltsville, MD, which is about a two and half hour drive for you (maybe less).
IMO staying at home and trying to find substantial stock that's worth the $$ online is a futile pastime and will result in overspending for underperforming stock.
www.driftwoodbonsai.com
