If you want the functional equivalent of the Hannon guns youd probably be better off either getting a used model 14, AKA the 6" K-38 target gun and having the barrel cut to the length you want, or getting a used 15 and getting a used 14 barrel (Ive seen them in the $75 range) and doing the work. Simplest and cheapest is probably the 14. Ive watched them on GB, they can he had in the $300-$350 range now and then for working grade guns with some finish wear if you are patient, same for the 15s.
If you have a fixed sight K, IF you can fine someone with the cutter needed for the undercut for the sight elevator nut, buy a sight, then get a 14 barrel and cut it, you end up with the same basic thing again. Anything is possible with money, its just a matter of your acceptable budget, how reasonably you can get work done if you cant do it yourself and what the alternatives cost to achieve the same end.
I like projects and am not afraid to do some basic stuff myself, but cutting a frame for adjustable sights isnt something that can easily be done at home without special tooling and machines and those that have them want real money to do it. If you have access to a mill and can get the rear sight nut cutter, it may be worth trying yourself.
Edit: Just looked around heres a 15-6 with heavy barrel. https://www.gunbroker.com/item/814847995