There is a permit process to dig and also a tag to buy and display to use public faciities like trailheads etc. BUT private land can be less of a paperwork hassel as long as you have the ok from the owner. They usually think it's funny that people wanted the stunted trees. My secret has been to find the owner's favorite breakfast spot in town and pay for his breakfast. This starts up a conversation/introduction. Most of the waitresses know who owns what.
Russ, my favorite tool of choice is a shovel but sometimes it has to be a chisel.
Carmen, nope didn't find anything. Bonsai, like koi....if I don't find something really special then I leave it be and walk on.