Jeff, do you know much about felt quality? I don't so err on the side of caution, by buying wool felt from an online company. There is a distinct difference between it and the felt you buy in craft shops and hardware stores, but I don't know how much difference it makes on valve padding. Heck, for all I know, the cheap stuff may be better, but I doubt it. I've been getting mine from www.achildsdream.com.
I have used felt from a variety of sources to include "vintage" hats from Goodwill and Salvation Army.
I also buy from Piano/Organ suppliers.
The stuff from Wa/mart and other hardware stores sell material intended to put ion the bottom of chair and table legs.. that is sturdy stuff.
Pool table felt is extremely durable but thin.. comes in more colors than green.
I do not know a great deal about felt except that a Swedish lady friend of mine makes her own for hats and it's the best I have seen.
Her process is hand knitting with 100% wool and hair from Camels and yuppie Camels (alpacas, llamas and vicunas) She then boils the finished piece and shrinks it. When completely, you cannot tell it is knitted. Looks like felt.
Sadly the hats are beautiful and $50 a piece so not likely to buy one and cut it up.
Might also talk to some Mongolian nomads as they make felt houses... possibly from yaks hair of steppe beasties
That reminds me,I once stayed in a mongolian yurt when I was wandering around in the mountains of catalonia! It was before my accordion days but I did get the squeeze on with a lovely argintinian girl. The place was run by mongolians and in the evenings we would play a game with sheep's ankle bones and drink fermented yaks milk, rode around on horses in the day, happy days.
Though I will not be tempted to start cutting up my stetson hat.