On Friday, April 6, 2018 at 12:02:45 PM UTC-7, wrote:
Available from Farm Supply stores, veterinarians, Tractor Supply stores.
Note: I use them, but out here in the high desert, where double-digit humidity is the exception, not the norm, the rubber donuts dry out and crack after a few months.

Fuel injector O-rings might work; they tend towards large cross-sections and small IDs.