You have some good suggestions for alternate sources for brushes, but I'll add a few more. When I need replacement brushes, my nearest source, a good hardware store is near me. They have a bunch of pull-out drawers with hard to find mechanical and electrical hardware. Two of those drawers contain a bunch of different sizes of brushes. I pick out a pair that is longer, but otherwise matches the size and shape of my original brushes. The wear end of your brushes are curved from use, but the replacements will be flat on the end. This is not a problem. They will wear to a curve with use. There is almost always something that will work, but brushes are just soft carbon, so sometimes what I pick need a little filing with a fine tooth file to narrow the dimension(s) a little. This is dirty, messy work, but it's not hard to do. If you ever return a used brush, placing it back into the tool, be sure to orient the brush so the curved end is again oriented the way that it was when removed. The curve orientation should match the curve of the motor shaft.
You could also try Grainger or other industrial Supply stores like Johnstone Supply if one is near you. An electric motor repair/rewinding service shop is another place to try.
Central North Carolina