Yes, an electric shop will have the brushes you need. Radio Shack, too, although I prefer our local, small-town, old-school hardware store. I've never stumped those old boys yet. I've taken in worn down things, parts of things and unidentified things, and every time they've found me new ones, the rest of it, or ID'd it for me. Take the brushes with you and say you want two more just like that, only new.
There's some wiggle room in length, since the springs compress.
A word of warning: Once you change the brushes, expect the motor to be clattery-noisy, probably for 10 hours of use or so. The reason is the new brushes-you're rubbing a new, sharp square brush end against the round commutator. Especially if you have the kind with the grooves cut in it; all that cleaning will clean out the gunk smoothing them out. As the brushes wear into shape, the motor will quiet down.