The canister "O" rings were made of natural rubber, white in color, in metric dimensions.

The Type I was 58.5 mm ID with a 3 mm cross section. (blueprint)
The Type II was 71.8 mm ID with a 2.5 mm cross section. (blueprint)

Very close white replacements are available from:
http://www.theoringstore.com/

The Type II stock number is WN70146 (measurement of metal canister).
The Type I stock number is WN70228 (per blueprint dimensions).

Neither is metric, but the Type II is within a few tens of thousandths of an inch. The Type I is a bit "fat" in cross section, and a tad "small" in inner diameter.

Both are 70 durometer, a bit harder than the original 55 durometer.

The good news is that these are very inexpensive. The bad news is that they have a minimum order, so you may want to buy a bunch and sell the extras.

Hope this helps someone.