Good riddance, IMHO. The " Duroflints" were terrible on frizzens, as the synthetic material would not fracture, or " knapp" off on contacting the frizzen. The result would be deep gouges in the face of the frizzen, that limited the number of sparks you got with each hammer fall.
You must be doing something very wrong to be having trouble with natural flint. Here's how to knapp flint with your own lock, so YOu can dispense with tht " knapping hammer " or tool you have been trying to use:
With the gun unloaded, and the prime out of the pan, cradle the gun in your left arm( right handed shooters with RH Locks) and use the outside of your thumb to lift the frizzen up while you lower the cock with your strong, right hand. You want to lift the frizzen high enough so that the edge of the flint will strike the bottom of the L-shaped frizzen, at the " heel " if you look at the " L-shape" as a human foot. Make sure you keep the rest of your thumb behind that face of the frizzen, but hold the frizzen open at that angle. Now, cock the hammer back, and trip the trigger with your right hand.
The edge of the flint will strike this sturdy "heel " of the frizzen, at a steep angle, knocking off a new, STRAIGHT edge across the width of the frizzen. A " Spawl" will be sheered off the bottom side of the flint, make for a very sharp edge that will last many shots, as long as the lock is tuned. Even if the lock is NOT tuned, you will get good sparks from a flint that is sharpened using only the frizzen.
This idea is NOT NEW. I saw it many years ago in Muzzle Blasts. My brother recently went through his collection of back issues, and found the article in the August, 1966 issue of Muzzle Blasts, at page 21. The article was submitted by a Paul Nichols, and is titled, " Sharpen Your Flint".I relearned the technique from a friend in my ML club, 15 years later, and I have not used a knapping hammer since. I am still trying to give it away!