I think you can buy individuals pins somewhere, but don't know the source.
I will warn you that you will tend to use other sizes than you think. For example. A friend
has a .44 S&W with accy issues. Pulling the barrel failed (!!!!!!) even with proper wrenches,
was risking frame damage, it is so darned over torqued. So, we are fire lapping. I selected
the pin gauge that would go down the bbl (which is how you find thread restrictions, too) and
we took it with us as we shot the abrasive charged bullets. We checked periodically to see if
the constriction was gone yet.
That pin for his gun is .418. So not only do you want the likely throat sizes, say .427 to .433 for .44
guns, but you need from about .417 to .421 for checking for thread choke, all in .44. Do the same
for .357 caliber guns, and .45 caliber guns.......you can see where this is going.
Plus, I think the individuals are a few dollars each (not sure) where the set works out to 3 for a dollar.
Whatever fits your needs and budget best.
Bill