I've been to Garden's Unlimited once. I showed up unannounced based on an old post I read that said they were open on Saturdays. Turns out that they are now open by appointment only, but they were nice enough to not freak out or call the cops on the stranger walking around on their property. They've got some really nice stuff there. My memory is a little hazy but I don't remember them having a lot of pre-bonsai stuff. It was mostly really nice, big, expensive stuff and out of my price range. I could have that wrong and it could have changed by now anyway. I haven't been to the other 2.
Another place that's open by appointment is Adams Bonsai in Lynchburg. He has some nice, affordable stuff and I found him to be very nice and helpful. He had JBP, Scots Pine, Azalea, Trident Maple and other stuff too. I would have liked to spend more time with him but he had someplace to be that day and couldn't stick around. I would definitely recommend that one.