TnAbout;
There's a very popular fly, that's been around for a while, called "The Golden Stone"!? It's a nymph, and quite a good one.
Does your father in-law mention if his fly is a wet, dry,nymph, anything other than just the name?
Unfortunately, almost every fishing area, with any sort of popularity seems to always spawn it's own "secret weapon fly"! Or, "name, specific to that region". Case in point, is the "St.Joe Special", a very popular fly for the North Idaho Panhandle region, where the St.Joe river is located.
However, the poor St.Joe Special, is also tied in about 50 different ways, with 50 different, fly fishermen saying; "Why, their version is the RIGHT version and WHY it works the best"!!
"The Truckee River Special",very popular for fishing the Truckee River in and around, Reno Nevada, is another example of the exact same problem......... 50 fly fishermen, mean 50, different versions of it available.
If your father in-law can give you any more information it would sure help in your search!
Good luck!
Paul