By the way, I'll assume you don't have land with trees on it, so here's how you go about getting some wood. You venture out in the country and try and find someone with some woods. If possible, find a farm with a hedgerow, they are usually long lines of trees between a couple of plowed fields. Often you'll see a number of stumps among them, where the farmer has cut fenceposts. You go to the nearest house and ask politely if you might be allowed to cut one tree for making bows. If you've made a bow before, bring it with you to show them. More often than not they will give you permission, and might even help you harvest the log. They might ask a bit of money, usually a fencepost runs $15-20 and an endpost (bigger, better log) runs $20-30.
You might also get some of the rural newspaper ad publications that have stuff for sale like cars, tractors, dogs, livestock and such. Sometimes you'll find ads for fenceposts, more often than not these are hedge (osage).
Might even call the local conservation office and ask them if there is any public land you could get to permission to harvest one log or even a few branches from. And keep an eye out for tree trinmmers in your area, I've gotten wood from them. Ask them where they haul their stuff, maybe your town has a municipal yard waste area that might also contain branches and stuff. Right after a bad ice storm there is plenty of wood in those.
American elm, red elm, hickory, osage, black locust, hop hornbeam, rock maple will all make a bow.