I generally keep a fair amount of generic parts and components on-hand. Why order one of something, when you can order 2, 5, or 50?
I end up doing several parts orders between the various suppliers depending on the state the game is in (anywhere between a former parts machine to completely dead to fully playable), and what is available from whom.
Bulk ordering usually saves me from having to make too many orders the next time, though.
It also doesn't help that I don't stick to one particular manufacturer or era. I have games from the 60s up through 2006 or so. Quite a lot of parts in a mix that large.