Source to shop hydraulic cylinder seals by size?

I've got a clutch slave cylinder that's leaking a bit and there's no rebuild kit available that I can find.  I can get a new cylinder and it's not tremendously expensive, but the bore is in good shape so if I can just pop a couple new seals in it I could save a few bucks.  I was going to try my local hydraulics shop, but as I understand it, the type of rubber that is compatible with brake fluid isn't compatible with hydraulic oil and vice-versa.  The seals look sort of like this:

I assume I'm looking for EPDM rubber and I can grab my calipers and take some measurements for the ID and OD.  Is there a source or a catalog to go searching for those?  Or even some sort of assortment like regular o-rings would come in?

I typically use my local bearing and seal supply house for things like this. They're way more than a hydraulic shop and they get the different types of applications that I need.

Beyond that, McMaster has quite a diverse variety of seals compatible with brake fluid...

https://www.mcmaster.com/products/seals/for-use-with~brake-fluid/

If you know what you are looking for you should find it here. Unfortunately, you are looking for a seal in a special rubber compound in a size that may have been designed and manufactured in Sweden. It's not so much the design/style, it's more the ID x OD x HT differences in US / EU / UK / Asia markets. What's really fun are the cylinders designed with a metric ID and a US Standard OD. I used to be in charge of International Sales as well as Marketing for Hercules so at one point I knew all there was to know about seals like the back of my hand. I'll do my best to stear you in the right direction.

This is my old company, Hercules Sealing Products. They are the largest aftermarket seal supplier in the US and may have the seal you need. If they don't, there are some other ways we may find what you need.

First, look on this chart and double check the fluid you are using against the seal materials available.
https://www.herculesus.com/oracle/files/reference-charts/Fluid_Compatibility_Table.pdf

To see their whole free option of seal technical information, look here.
https://www.herculesus.com/page.php?name=Reference-Guides&id=306
and here.
https://www.herculesus.com/page.php?name=Technical-Library&id=304

Rubber based seals often swell when they've been subjected to water, so if possible it is best to measure the metal gland the part is going into. Here is a reference diagram for the technical terms you're going to need. Although the page says urethane seals, that more deals with the dimensional tolerances. You're going to need to figure out Seal ID aka Groove ID (Piston groove OD in a piston application) x Seal OD aka Cylinder Bore (Rod Gland OD in a Rod application) x Groove height (same for rod or piston applications).
https://www.herculesus.com/oracle/files/reference-charts/Groove_Dim_Chart.pdfc.pdf

And that's pretty much where your fun ends with the Hercules website. It looks like they took down access to the product lists unless you set up an account. You could get your measurements and call their engineering department and tell them what you are looking for with the dimensions. Don't call sales, they won't know enough and will route you to engineering anyway. If possible, ask for Ahmad Muqbel. Tell him John Hoopes gave you his name and said he was the nicest dude ever. Hopefully, he can help you track down the exact seals you need. I left there in 2000, he should remember me.

If that doesn't work, let me know. I still have contacts overseas.

In reply to hobiercr :

Wow, that looks like exactly what I need!  Thank you so much for that - I'm going to do some careful measuring and it looks like they've got what I need in their catalog.