The best collection of photos is in Henry of Boulton: A Pennsylvania Gunmaking Family and its Firearms (Jacobsburg Historical Society, 1988). You can typically order this directly from the Jacobsburg Historical Society for (I think) $15.00. But they are between Executive Directors right now so it is a bit more difficult to do so than usual.
If you do want to obtain a copy, feel free to email me directly (spg4@lehigh.edu) and I can find out the actual cost and how you can obtain one.
Scott