Not sure if they would be large enough but the lead like covering on the top of a bottle of wine might work. Bonus being you may have to go through a few bottles to get it right.
A normal rubber will tend to spread the graphite rather than lift it off. Artists use a "putty" rubber which is a lot softer and lifts the graphite. Got to an art supply shop, they are not expensive. As an alternative, take some new blu-tack (other brands are available) and work it with your...
About a year ago I got a Fengda FD-186 for around £80 off Amazon. Dual action with moisture trap, pressure regulator and tank. Works just fine. I got this for painting model tanks and found a load of advice on military modelling sites and YouTube vids showing what the various features do, and...