Have all you respondents that are recommending sources for O-rings
really read the OP's post? He doesn't want an O-ring, he wants TWO
O-rings, of different diameters, *connected* by 3 radials, all as ONE
unit.

I'd think a decent machinist could make an aluminum mold for $150 or so,
if you can find some liquid O-ring goo to pour in there. A couple of
flat plates, a ball end mill, an entry level CNC, and you're done. Hell,
you don't even need the CNC if you know how to use a rotary table, but
it takes longer.

MIght need to spend a little time with an X-acto knife to trim the
flashing.