Once in a very great while a Miroku comes up for sale on one of the Internet auctions. But it's rare, and they seem to sell quickly.
That stock, mentioned above and any spare parts might be a good starting point. As also mentioned just about any type of barrel can be duplicated. But be prepered to wait a year. Also, the pans on the originals were either forged with the barrel or forged welded in place with a keeper. Would be an expensive barrel. The lock (as locks go) would be relatively easy to make for an experienced locksmith.
If you have to commission all the work and assembly to a gunsmith, could get rather pricey.
Another option is to purchase an original. The plainer ones with little/no decoration can often be had at a reasonable price. The barrels on these guns are usually heavy walled octagon. The barrels can be easily burnished and the lock may need a little work. But then you will have a safe shooting original for probably less than a custom replica.
I notice you live in Maryland. The largest antique arms show is in Baltimore every March. I've noticed quite a few plain originals for sale there evey year.
Here is my original that had just that type of work done to it. Just a thought.
Yes, the sights, especially the rear is very unusual. They were made to insert seperate, different inserts depending on the anticipated range.
Rick