Hi Bobbie,

You can buy regular felt and cut your own - https://www.cramersportsmed.com/felt-variety-pack

Or you could buy the hoof sock replacement ones - https://www.theconnectedrider.com/hoofcare/the-hoof-sock-felt-replacement-pad-m/

Or check Michael's Crafts although they sell much thinner pieces for crafting so you'd probably have to do a bit of gluing to get the thickness you want.