Master cylinder questions

I don't know where to buy the rubber bushing separately. If me, I would try to use a thick rubber O-ring, but I have an O-ring kit. I think its only purpose is to keep the brake rod from rattling, but I would try pulling the brake pedal up and see if there is any way the rod could pop out of the MC, since some people say the bushing retains the rod. I don't recognize the spring. It doesn't quite look like the spring in a wheel cylinder kit.