Ive rebiult dozens of these things, and alomost every time at least one of the bearings gets lost.
McMaster-Carr has bearings, any size, and alloy. 2mm is what you will be looking for if I remember correctly..
http://www.mcmaster.com/param/asp/psear ... ;121=102746 bucks for a hundred isnt bad.
Ace sells O-rings.
Metric or standard, they have the right size you need. What I used to do is just take the whole barrel assembly and valve with me, and keep trying out diferent ones untill I found find a size that sits tightly in the groove, and fits snuggly when the valve was shoved into the chamber. I coulnt ever remember the number, so Id usually buy five or six at a time.
The last one I rebuilt, I used the green HNBR air conditioning O-rings, and it has never leaked once. That was nearly a year ago, and the last time I used it was nearly six months ago. Its probably still holding the gas I last filed it with, wherever the thing is.