I got the meat from Weee; I'm pretty sure it's not kosher but I can't say I looked for a hechsher. I've seen cow feet at many different stores locally, though, just not ones that would typically carry kosher products. Apparently the dish is supposed to be made with veal feet, but that I think is actually illegal to get in the US or something? I remember looking a few years ago and calling around for it. If you're specifically looking for kosher cow's feet, I have absolutely no idea how you might find that unless you know a kosher butcher shop. Here in the Boston area I'm not sure there are any, and I've never checked the one actual kosher market for cow feet.

Looks like you can buy it online: https://www.aviglatt.com/cow-feet-1-5lb-pack That's expensive, but I don't imagine this is an everyday dish so it might be worth it?

If you can find kosher chicken feet, which might be easier, I dunno, I hear you can also make a good chicken ptcha, but I haven't tried it. And cow's feet are great because of all the collagen, but you may be able to do something similar with something like a rack of ribs if you simmer them long enough. Good luck!

For the record, my mom's Ashkenazic, with family from mostly Ukraine, I think, and she grew up with traditional Ashkenazic food. She'd never heard of the dish when I sent her a picture of what I made. My dad's Sephardic so he definitely wouldn't know, but I kinda expected my mom to have come across it at some point. Maybe it was always a very local dish?