Thread: threading odd muzzle

I have this .22 with this odd muzzle that I want to get threaded for a suppressor. I don't want to cut the muzzle off for a traditional external thread, I'll need to thread internally and have an adapter made but the two local hamilton gunsmiths reckon they can't do it. Have no interest and time in posting and filling out police forms to send to a smith that may be able to. I thought of trying it myself, I know how use a tap set and have some engineering skills to make a crude adapter but a bit nervous that I may get it all on the piss. Anyone here in the waikato got the skills and tools that could help? Thanks.