I think you would have a hard time finding an actual recoil pad. That said, I bought a Boyd's stock for my 10/22 and was pleasently surprised that is almost perfectly took a Savage 110 Limbsaver pad. Did I need it for recoil? No, but it sure helped for grip and length of pull. So... If you carefully measure the width and height of the existing stock, you might be able to find a pre-fit pad for another gun that comes really close. I believe most of the pad makers have a PDF of the dimensions of all their pads to help with this sort of thing. If you get one that is oversized just a little, 20 seconds on a belt sander and it will be trimmed down flush.
Alternatively, yes, glue on a chunk of rubber. Pretty much anything can work, from old coveyor belts, to mudflaps, to old sandals. It should be easy to glue it on and then trim it flush.