John -
Have you considered CDL for tailing material ?? I think it would meet the criteria you mentioned.
Whiting used to put out CDL packs in three color ranges with three clumps per pack - about a lifetime supply for a casual tier, and most likely still does. As I recall, a pack runs about $14-15. You can also use it as a substitute for quills or biots for the bodies on very small flies. Tough stuff, and pretty easy to work with.
John
P.S. Enjoyed your anecdote about fishing the Yellowstone and playing with that big brown. Reminded me of a lot of days I spent on the South Fork of the Snake when I lived down in SE Idaho. And a big brown that I caught, and lost, downstream of St. Anthony on the Henry's Fork. But I lost that one quickly - one of the great ten second memories of my fly angling experience.
The fish are always right.