My local Canadian Tire does sell gasket paper, but have cut down on the number of thicknesses in recent years (their selection now sucks in the worst possible way (one thickness only), it could only be worse if they didn't stock it at all).
Try a google on "karropak gasket paper". It comes in 1/64 and 1/32 thicknesses and quite possibly others as well.
An interesting thread on gaskets (for use in carbs - but the basic info transfers to other uses) can be found at
http://www.smokstak.com/forum/showthread.php?t=89564
Post 13 in the thread shows thicknesses available and part numbers (for example FPG 3045) and the price the poster found at NAPA a couple of years ago at the time of the posting.