Moonman,
You might try "Prarie Point Junction" in Cozad, Nebraska. They have wool felt by the roll that might work. I'd try a sample first though to be sure. The color that is closest is "Cobblestone" WCF2615, but they say it is limited quantities because it is discontinued. Alternately, you could us "Driftwood" WCF2619. I have no experience with this felt, so I can't recommend it without reserve, but it looks to be suitable.
Frank G.