I can't speak for blower brushes, but here's my experience. Three years ago I was living on the east coast, I pulled my heater box and took the top half of the heater box with the fan to P&H Auto Electric in Baltimore. They rebuilt my heater fan motor with new brushes, balanced the blades, all for $50 plus tax. They are an old school automotive electrical shop, hard to find these days. https://phautoelectric.com/