My local guy doesn't charge much and rarely needs spare parts - his take is that the vibration on a bike is the main problem and he just strips them , cleans and lube's what needs it and reassembles them, screwing them up nice and tight.
He fixed two non working rev counters for me for a $60 each, less than a quarter of the $300- Oz "Expert" charges for one , and the expert usually wants $100- quids worth of parts too.
Getting the rim/ glass off without damage takes a bit patience, but they are available new, just cant remember who from!