I came across an NOS Ever Ready C40 boar brush. I soaked it in some conditioner for a few hours before the first use and it was good to go. That was the recommendation from many on this forum, so you might want to try that first to soften up any brittle hairs.
On many of my restores even thou the original brush may have had white on black (Rubbersets), I re-letter them with yellow or gold.