you can also look for some other plywood - I often use beech plywood, which is also regular in German home stores. Beech ply is harder than birch ply, heavier and looks a bit darker. Also a bit more expensive, but sells good, so that should not be a problem.
You should also check out local professional wood workers. As we have mostly small projects and they do big projects, they often have rest pieces for a few $ tip. They can plan them down easily, as they have the professional machines for that. You might need to store that wood then for a limited time.