On the same vein as above. Don't drill the brushes, just the holders. Push the brushes back past your newly installed retainer pin. Slip the brush unit in place then pull the pins.
GM used this, and it was built right in to the alternators. Was sized for the plastic spray can tips (like wd40). Was a benefit for the not so brite techs as if they forgot to pull the pins there would be no short circuit.

Did you try any of the motor repair places or small appliance shops? Be willing to bet they would have a better shot at getting you the right brushes. Or at least the correct style and composition. Easy enough to sand down them to size if need be.

Just noted after doing a little surfing, there are 4 grades of brushes. You had the graphite/metal version originally, not sure how well/long a straight graphite version is going to work.