My best source is a local lumber supplier that sells to woodworkers and furniture builders. They have small pieces of rock hard maple for use in making cutting boards.
I find a few boards that have straight grain and I rip it on my table saw. They may machine it for you if you ask nicely.
Or find someone that puts in hardwood floors. A few scraps from a gym floor will be a lifetime supply.
balsa USA has it!
https://shop.balsausa.com/category_s/3875.htm Dad was a mater carpenter, so I got a few skills from him.
Also consider Beech or birch if you cant find maple. It woks fine.
Had some scraps from making drawers that made several flite streaks
Stay away from soft maples, any species of maple wont do.