"Most music stores hereabouts didn't even carry thumbpicks and fingerpicks, only flatpicks."

What a desolate image! I'm glad you've found a source.

In 1973 my brother moved to Mansfield, Ohio and discovered that it was impossible to buy spinach noodles. He finally located the rice in a gourmet food section. He felt the way you must feel with respect to fingerpicks.

My thumbpick is an M. All this week I thought it just had two parallel marks on it -- some kind of cabalistic code -- but it's merely an M that went over the edge of the pick.

I don't have to worry about fit because the thumb pick is the only pick I use. My other fingers play au naturel. I play the dulcimer rather as if it were a piano, with a lot of finger independence. When I want a strum, I brush the thumbpick over the strings.