Several years ago I helped out a neighbor with his.
I had some sort of polyurethane laying around about ~1-1/2 to 2" dia., durometer unknown.
I cut it to length & stuck in the freezer to machine it.
Placed a aluminum rod in the ends of the walker legs with the ends tapped for 1/4-20, and fastened them.
C'bored one end of the poly to fit over the leg and then c'bored the other end for a 1/4" flange head screw.
Had to toss the pieces back in the freezer constantly.
Held up well and gripped the wood deck and pavement/concrete very well.
The only issue IIRC correctly is that they picked up 'grit' outside and he had to rub them across a mat before entering the house.
Sorry I don't know what type of urethane it was.