Thanks y'all.
None of the auto parts stores have the Viton o-rings in that size. The biggest they all had was 19mm.
I found them online and ordered them. 5 bucks shipped for 15 of them. I thought they'd be more than that but I ain't gripin'.
Thanks for the reminder about the generic parts page. Don't know why I didn't go there first.

I'm glad I saw those pics, or I may have very well wasted my time using the standard o-rings.