Could you make one from a Pedersoli SxS black powder? I don't know the legalities of cutting down shotgun barrels on black powders. Most of the ones I've seen have straight grips.
I wouldn't want to mess with shaping out the locks, so maybe cut the wood off behind the locks and make your own grip.
It would be neat as a project if it's legal.
Of course, we're not talking about a tack-driver.

I think the name comes from:
"Howdah hell do you hit anything with that?"

As far as I know, in the state of Iowa, there are no regulations concerning black powder pistols/rifles, whatever, like there is with the modern, cased ammunition weapons.

I've always wanted to try this, too. I'd also like to try making a hand-shotgun to be used for shooting rabbits and birds. I understand the accuracy limitations, but it would be fun to do, imho.

It is legal to cut off percussion or flint shotguns. At least as far as batf is concerned. They aren't considered firearms according to GCA'68. Of course, if you're considering this it'd be good to drop a note to the Batf BEFORE you take hacksaw to steel. I have a saying, "it's often easier to get forgiveness than it is to get permission." This applies to my wife, NOT the BATF!

It's not a project I will be embarking on any time soon. I will send a letter to the BATF and ask them.