Hey Jim, welcome to Bnut! I'm glad you're looking into eastern hemlocks as bonsai, it's good to know at least a few people are haha. So I started getting interested in bonsai last winter, and now I'm hooked of course. One of the first few tree species I looked into for potential bonsai was Eastern Hemlock as this is one of my favorite tree species in general, they're absolutely stunning in the forests around here and I've seen very very old Hemlocks in patches of old growth forest in the Adirondacks that are just huge.
So you can imagine how let down I was when it was incredibly hard to find even a few examples of people working with this tree and even on this forum being told they're next to impossible to work with, or at least that it would be a fight the whole way. BUT I love this species so I'm going for it anyway. Lancaster's tree is one of the nicest I've seen, so that's kind of an inspiration to go for it.
As Nomad mentioned they're especially finicky with soil, but I think the bigger issue is actually finding a suitable tree to collect in the wild. This dawned on me when I went for a walk in the woods this past spring to scout out hemlocks that were suitable for collecting. And I left the woods convinced that they don't exist!!!! Basically the issue is that with most any wild growing Eastern Hemlock, the foliage or even first branch is SO FAR from the base of the trunk that the best bonsai you'd ever get out of the average tree in the forest is a 5 foot tall trunk with a bit of green at the top. And as far as I understand, Hemlocks don't really backbud much, but I could be wrong.
BUT, all hope is not lost... this goes back to what nomad was saying about searching for those very few hemlocks that are growing in adverse conditions that may be naturally dwarfed. So I'll conclude my rant now, but I just noticed most of the trees in your pictures do not have foliage anywhere near the base of the trunk, though some really interesting trunks and trees! But regardless, you would not want to collect anything like that, but search around as much as you can and see what you find. They're out there somewhere! They've got to be!!!!
I have yet to find a suitable hemlock in the wild, I really only scouted in the forest a couple times, but I plan on checking out as many areas as I can next spring. If anyone knows where there are some scraggly dwarfish hemlocks in NY I'm all ears.
Though I did manage to buy a small hemlock from a nursery this past summer, maybe 2 feet tall with a decently thick trunk, and with much thicker branching and foliage than what you would normally find in the wild. Haven't done much with it yet, but I'll snap a photo and post it up here tomorrow. I'd love any suggestions or advice.