I understand the "take what you want" response in rural areas. I'm from a rural area myself. I've learned that things like this really don't make that much difference to most people UNTIL they do.
In my neck of the woods, if you're digging on someone else's land without permission and that person is not all that sociable or understanding, it's a good way to get a butt full of birdshot...Everyone I grew up with in western Va. (and in Texas) was armed...Best to seek permission before digging, especially in the South, at least that's been my experience. If there is an association involved, definitely seek permission. I've been on association boards. Some board members can be, well, little tyrants...
As for collecting these particular trees, if permission is not hard to get, why the rush? If you've never collected oaks, why make these nice examples your "learning trees?" Why not find some lesser trunks of the same species in the same area and collect those to learn what you're up against as far as tap roots, soil and other bugaboos that happen locally. Understanding those locally specific things goes a long way towards getting choice specimens like these out alive.
You're probably not going to get all that much advice from people who have dug eastern oaks for bonsai, as they're not all that common. I've dug White Oak (quercus alba) and willow oak (quercus phellos). White oak species (there are more eastern oak species that considered in the white oak family) are not that easy to dig, although they're a lot easier than conifer species. They are not forgiving in the root department. They usually come with massive tap roots that don't like to be disturbed, at least all at once and feeder roots have to be tracked to the finer ends.Once you get them into a container, they act kind of strangely. Bonsai leaf reduction techniques, for instance, like leaf pruning, can result in larger leaves...
Willow oak is much easier and more forgiving. I don't think those are willow oaks, though.
