Knowing where to look is the important thing! We often forget that a bonsai tree is a tree that can be found in our surroundings! To get a tree worth doing, you have to look in a place which is inhospitable to the species. It causes them to do exaggerated things to survive. So try and find a place which is hostile to trees, but still has them... and then find out who owns the space. Most land owners don't really care about what's on the back 40, and would likely be willing to let you take out the trip hazards that we love. Often times, if it's state land, you can get a "logging permit" to take out small trees.
That's why places like high mountain areas are most suitable to find a lonely and strong maple tree that suits to bonsai.Very inhospitable place where trees eek out a bare existence over hundreds of years.
In this video you can see an expo in Japan from trees mostly collected from nearby woods of the region. These aren't bonsai trees that have been grown from seed, or at least most of it has been taken out from somewhere..
Good luck in finding your own bonsai !