My favorite source of Canadian silver dollars are from my local N.S.N.S. coin club with their coin auctions at the end of the monthly meetings in Burnaby. There's always a few on the auction table from Collectors that are supplementing their retirement income. Most of the time they're a bit under spot.
I usually save up and buy from the junk bins at the bi-annual coin show, but it seems like saving and waiting doesnt work now. So I kinda just DCA every month now.