Moconfed, exactly what are you looking for? There were no standards, as I'm sure you are aware no two were alike. Once you decide what you want you can contact Rayl, Colerain, Goetz or any of the other custom makers and have it made, no problem. Decide on caliber, length, width at the breach and, probably most important, rate of twist. Decide whether you will want to shoot a round ball or a picket ball and, if the later, whether you will want a false muzzle to help in loading as was done at the time. Ed Rayl might be your best bet. Also, if you use a picket ball, you will need to have a custom mould made.
I'd prefer a 50 cal., at least 36 inch. 2 inch diameter hexagonal. Round ball. Twist, I'll have to sort out.
I spotted one a few shows back that was rough, but serviceable (and 42"!) Should have snagged it.