Cannot comment on the Youtube video without a link to see the specifics of what he's doing.

Motor brushes are not supplied as spare parts. Whole gearmotors are, and depending on availability just the motors upon special request.

The fans are 12 volts also, so you'd have to swap them too. There is no reason to run the motor, fans, or stall protection board at higher than 12 volts. If more heater power is needed, get a 15 or 18 volt supply and use it to power the PID controller and heater. This has been done and discussed on the forums:

http://www.soliforum.com/topic/12567/in … mperature/

18 volts is double the heater power that is produced at 12 volts. That is enough to get to ~400C, the thermocouple should be upgraded at anything over 260C as that's when the PTFE insulation starts to break down.

Where can you buy new brushes for the motor?

24V is not much higher, i would bet it works perfectly for the life time of a filastruder. The rating itself does not mean that nichrome wire is too tiny gauge to handle slightly (in this case 33%) higher voltages, albeit MTBF is going to be shorter ...
Perhaps get a replacement tho before trying how it functions.

So my question still remains, what is the maximum voltage for the anti stall PCB?

Motor cannot run at 24v without extreme brush wear.

It would be convenient to convert to higher voltage if just the brick can be replaced

This would allow me to run higher temps with nylon based material experiments .. and graphene, and some other fillers