Might be cheaper to just rebarrel the rifle with a quality barrel,Green Mtn,Badger ect.keep the old barrel if the rifle has some significant provenance.
You will most likely have to contact a barrel maker and ask them.Lots of B/P barrels out there that were made with metals not suitable by todays standards for any kind shooting.Most gunsmiths do not have have the equipment to rebore barrels,very expensive.Do a "Google Search" and you will find barrel makers that might be able to help you.