Will try to give you some sort of answer, but I'm not sure from your description what you are trying to do--barrel wise. Are you replacing the original barrel? If so, then Track of the Wolf or Cain's Outdoors or any other muzzleloader supplier can provide you with a breech plug. If you are using the original percussion barrel, you would have to find a touch hole liner big enough and with metric threads to replace the drum. Haven't done this, but assume that there is a liner available from the same outlets. That being the case, I am not sure why you would be wanting to replace the breech plug. I am by no means an expert when it comes to this and am only thinking logically. Someone else on the forum will have probably done exactly what you are doing and will know if the answer I gave is good or not. Hope this helps or at least gets the suggestions flowing for you.