HF carries a multipack of metric viton O rings for about $6. They usually have a few sizes that are "close" that I've used with no issues on a few of my bikes. Also grainger/Ace hardware have about everything too. Google the part number and look around on the web. You can usually find the exact size info somewhere and then cross reference it.
Found it, thanks. Looks like they're in stock local too, I'll go pick up tonite.