I couldn't find much online other than discovering Ace Hardware is a retail consortium - a buying group that isn't big on spare parts for the stuff they sell.
If you bought the saw locally you might have more luck approaching the local outlet. Such saws are often bought in from a generic source (often of far eastern origin) and label engineered, consequently there are usually few spares available though many such saws arrive with spare brushes in the box along with a wrench and instructions, etc.

All is not lost as there are companies dotted around the world specialising in motor repairs and making brush sets to order from a drawing or copying a pattern. I bought a such a pair a couple of years ago for a very reasonable cost.