This is a standard O-ring, as metric O-rings go. There are about 500 inch size "standard' O-rings that are used in 99.9% of inch-size machinery... but a multitude of metric sizes - thousands and thousands of sizes. The one you want is a P-8 size JIS standard O-ring (7.8 x 1.9mm), they should be available from most industrial suppliers. There are still a lot of JIS sizes but this one isn't a real oddball, at least. You just need gas-proof, viton is probably best. You'll probably run up against a minimum sale, but that should be less that their minimum and shipping. Where are you in Canada? I know a good O-ring shop in Toronto.