Locks of this type are relatively easy to make for a skilled blacksmith. Time consuming but not difficult. From what I have read, the basic design is French and goes back to the 15th Century at least. That is not say those locks are anywhere that old. How old is the house? Does it pre-date the French and Indian War? Ed Donaldson has a website of antique lock hardware he sells and would be the one to ask about value. Scott, I have just found that James Patterson was listed as a lock maker in Pittsburgh in the 1815 directory. Doug