I am working on an all hand made lock made in the 18th century manner, and what you want is the Journal of Historical Armsmaking Technology Volumes I and V. Gary Brumfield, of our little family here, wrote two articles on how they made locks in the CW gunsmith shop. The instructions are complete enough for someone with the skills to make one. The first article in Volume I walks you through the whole process. The article in Volume V corrects the process for making the cock. The process in Volume I did not take into account the grain of wrought iron and resulted in a lot of broken bottom jaws. You might still be able to buy Volume V from the NMLRA. There is no way you are getting a Volume I. The photo ready manuscripts were lost to the first few volumes, so additional high quality copies are not possible. The other problem is that they were poorly bound and almost all of them are falling apart. I know mine are.
The problem with scanning them is that you can't scan a printed photo without an artifact that seriously degrades the quality of the image. Now, I am sure that there are a lot of folks that would like to have a copy of what ever quality they can get. I have scanned pictures out of the books for my own use that aren't too bad. I am sure I could improve them in Photoshop. There are probably re-touchers and restorers out there that could fix them all so that they look as good as the originally printed versions. The problem is that those people get $250/hr for their time and each image might take hours. I think that makes a reprint cost prohibitive. However, scanning and image processing technology improve all the time. There may come a time that the books can simply be disassembled and run through a scanner with no other input required.
Hopefully, Gary has provided the necessary legal permission to do just that to some party who is likely to survive him as the current U.S. Copyright law has gives the creator the copyright for his/her life plus 70 years. If arrangements aren't made before hand, that could put a lot of these out of print books out of reach for a very long time.