Or you could just go to the experts -

http://autoharpworks.com/felt/40-felt-strips.html

My London-based friend Wendy Grossman has a page on autoharps which includes a couple of other sources for felt , and also mentions the possibility of altering the chords by adjusting the position of the felt strips. "UK Autoharps" seems to have disappeared, but Elderly instruments (USA) might supply UK.

Wendy's page -
http://www.pelicancrossing.net/autoharp.htm

Might be worth contacting Hobgoblin, though their on-line site doesn't list felt.

Ross