Found a few threads where Mike's name got mentioned in relation to shotgun barrel threading and forcing cone lengthening. He was apparently still in business as of last year, but with Gov. Baker's ordering of all gun shops closed, I have no idea if he's open. But I can find that out by calling...
If you let us know where you're located and some details of what you have and what you're looking to accomplish we might be able to give you better answers.
I believe Mike does stock as well as barrel work, so figured he might be a good resource IF it was a shotgun the OP was looking to have "fit".
OP is kind of vague.