Replica parts don't fit original Sharps Pepperboxes generally.
Try Dixie Gun Works - they sometimes have 'some' original parts, but remember - their spares came from used weapons.
These are easy to work on - I've cleaned and repaired dozens - but I really won't suggest that you fire one, unless you're using CB Caps.
Modern .22 Shorts can be too much for the piece to handle reliably without damage.
Good Luck!
Vaya,
Scouts Out!