There used to be a company at the foot of granville and SW marine in Vancouver that made gaskets for industry. They had a whole warehouse full of gasket stock in all sizes and thicknesses. The name escapes me at the moment, but it should be in the yellow pages.
Or if you want to mail order there is
www.mcmaster.com
they ship duty free and brokerage free through Purolater at a reduced rate. Great place to mail order anything hardware related.