I would think soft as well but that is just an educated(questionably) guess. If I couldn't source one and had to make one from scratch, intuitively I would be inclined to turn one down from a piece of brass round stock or perhaps even aluminum on my lathe. Brass to resist the possibility of corrosion. But like I said OFB, that is only a WAG.
Hopefully someone with actual knowledge will chime in.
Craig - AKA Some Clueless Idiot
The person who is saying something is impossible should not interrupt the person who is doing it.