Not Welsh, but at least Celtic, I bought some goat's cheese from Cornwall bore'ma in Waitrose.
Brand is Trevarrian Cornish Creamery, and it calls itself "Gevrik Goat's Cheese".
Catching a glimpse of a French goat's cheese on the shelf, I was reminded of the French word, "Chèvre".
I admit I had to look it up to remind myself that the Welsh was "gafr" (feminine)
Origin and Etymology of chèvre
French, literally, goat, from Old French chievre, from Latin capra she-goat, from caper he-goat
So presumably the Welsh and the Cornish are also from that Latin origin.
But back to Welsh produce, I'm happy to say that there is at least one Welsh food item that I'm reliably able to buy in my local Waitrose (here in England): Rachel's menyn organig (wedi halltu neu dihalen).
They usually also have halen from Ynys Môn.