If you can't get them anywhere else, head on line to www.mcmaster.com - McMaster-Carr. You can get just about any O-ring in any type of compound you need, though I think that good old Buna-N (aka neoprene) will suffice for our needs. Just type in 'O-Ring' in the Search box. You'll have to sift through some of their stuff... they have a lot of items. But, a well-stocked hardware store should have what you need. THe fit doesn't have to be precise.. just snug around the carb barrel (as opposed to too loose).

Just $.02 more

Bob