I wouldn't be holding my breath for a repro to be built - despite the hype.
That said - for these guns, and for many others, replacement parts reside in someone else's firearm.
Never reaching large production levels, Merwin, Hulbert parts have always been in short supply.
Your best bet is to cast a wide net among every parts dealer you can find who deals in older firearms - you may get lucky.
You may not.
Personally - 'I' would save my money and add to the pile in order to buy a decent revolver that's complete and not cobbled together.
Good Luck!
Vaya,
Scouts Out!