What are these things called?...and where can I find some

I'm refurbishing an Angram beer engine and I need to replace the seals for the cylinder. The only problem is that I can't find out where to buy them or what they're actually called. I talked to the guy at UK brewing and he was great, but he said that they'd be out of stock for probably a month or so. Also, it seems like these sorts of things should be easy (and probably cheaper) to find via McMaster or someplace similar, but I don't know what to search for. Clearly, they're not O-rings but the correct name eludes me. Anyway, here's a picture. You can see why I want to swap them out If any of you guys have suggestions on what these are called and where/how I can find a few, I'd definitely appreciate it.

flat orings?

O-Rings, Cordstock, and Accessories

B

Check the yellow pages or the net for a seal manufacture they are out there that can custom make one but can be costly or wait a month from your other source. I had a couple custom seals made for a power steering box input shaft that was no longer available for only $48 and glad to have them.
One as a spare. Yours looks like a step square ring, thinking if it can be built up by adding two square rings or get lucky with one square ring.
Check a bearing supply house as they should have seal catalogs or a source or company to go to. Hey good hunting get it pumping again.

If the guy at the UK brewing place had some, why not ask him what they're called? Maybe he even has a part number. It looks like some kind of gasket to me.

Looks like a cup seal-the same sort of seal that usually comes with a steel retainer on the OD, like an axle seal on a car. Get the exact measurements of the shaft's diameter for the seal ID, and the body's inner diameter for the seal OD. A local bearing and seal company should be able to fix you up. Buy a couple.

Cool, thank you very much guys. I'll check into these suggestions and see what I can find.