Back in the 1970s when I first visited Williamsburg my two favorite shops to visit were the cooper's (for the aroma) and the gunmaker's shop. Even then the gunmakers were back ordered for at least a year since they built every one completely from scratch.
"The Gunsmith of Grenville County" is a good book on the subject. In addition to step by step instructions with lots of good pictures it also goes into the history of the Longrifle and profiles a number of the early Pennsylvania and Maryland gunsmiths.