What I use is old worn out Automotive disc brake pads. When I say worn out I save the ones that still have enough pad thickness for mower blade brakes.
I use a cutting disc in a right angle grinder to cut to size. Wear dust respirator, it's asbestos and metal filings.
If the metal backing is not needed heat the metal and the pad will fall off. If I need just the brake pad without the metal backing I drill a recessed hole for a small pan head screw. If the metal backing can be left attached I just drill a hole through the metal for a recessed pan head screw.
I make several at same time.
But if you can find a replacement brake just buy.
Get ready for sticker price shock.
If it's my own equipment I sometimes just remove the brake assembly and operate like the old style chainsaws without a chain break. I also sometimes go really bad and rip that tag off of a mattress that is illegal to remove.