Many of the free target websites have excellent patterns to print off, if you are shooting a scoped rifle, which you are not in this instance.
Take a Vitamin C bottle, approximately 3", and use it to trace out a larger sight in circle with a Black Magic Marker. It is large enough to see up to 100 yards, and dirt cheap if you have a printer to copy them off. For fine tuning use a Vitamin B bottle, about 1 1/2" in diameter, to do the same. I can still see the smaller dot at 100 yards, but it takes much concentration, yet this way I know the rifle is ready to go.
I make some in Red or Bright Orange, but Black still seems to be the best color to designate over the sights on my Muzzleloaders.
Beautiful rifle you have procured. Just a lovely job of craftsmanship that is satisfyingly useful.