My felt came from a leftovers bin at a gasket company many years ago. It is just a tiny bit thicker than the stuff sold commercially or that comes on a new harp, but it is a lot 'stiffer'. It never seems to get those grooves that happen to the usual type. (It is grey, with a reddish center stripe)

I probably have 'close' to enough to refelt one instrument, but I still need to do 3-4 bars on my current one. I never did finish the minor chords.

   When I found it there was no such thing as the WWW and Google, and I have never looked until now, but it only took me a minute to find this...
http://www.auburn-mfg.com/products/felt-gasket-material.html

I have not sorted thru all of it, and there ARE other hits. If someone wants to have options, I'd bet you can find something.