Both my local Suzuki and Yamaha dealers are good at ordering in anything aftermarket, and obviously, the Suzuki guy gets me any OEM parts I need.
I have also ordered stuff stateside from Dennis Kirk, this last time I had it shipped to my in-laws as we were in Phoenix anyway. They seem to stock lots, and shipping is prompt.
I've bought stuff in the past from Blackfoot in Calgary. Pretty good selection for a shop. And back in the 80's, Walt Healy in Edmonton was pretty good...(that was quite a while ago). Back in those days I was trying to source Bultaco parts, that were getting scare...