You are just the guy, Fred, to answer a VERY important question.
From the 40s through about 1985 someone or several someones manufactured long-bladed thumbpicks that were only about a quarter of an inch wide from the loop though the blade.
The best ones were parti-colored or imitation tortoise shell. (Folks say the color doesn't make any difference to the picking surface, but they're wrong.)
The last time I found any of these was deep in the Arkansas Ozarks back in the early 90s.
Thom Bresh has told me that his dad, Merle Travis, favored them, and he added that no less a picker than Scotty Moore has been searching for these things for years.
I used to work at a university, and me and another player there even had exchange students scouring the Far East for Japanes copies. No luck.
These were wonderful thumbpicks, with just the right combination of stiffness and "give." But apparently they have disappeared from the face of the earth.
Any help appreciated.
Best wishes, Tony