I suspect you haven't been looking to the right sources for your supplies, nor analysis of your existing mortar nor bricks. Obviously you have not yet tapped the abundant weath of knowledge of your local regional experts. I had NO problems sourcing materials for slaked lime via suppliers in the greater Allentown area. There are dozens of NPS properties in PA that have had PA contractors working on restoration of historic masonry. None of this restoration masonry work was done with hydralic lime based mortar nor portland (cement) containing mortar - but with (matured) slaked lime or lime-putty based mortar.
Perhaps you could start by contacting Bluebook of Building and Construction and order the Eastern PA & DE Edition source book for some preliminary sources for contractors/suppliers for Restoration & Preservation -- Historical Landmark and/or masonry, preservation or restoration categories and or mason, contractors & suppliers. http://www.thebluebook.com/wsnsa.dll/WS ... cache=3513
and/or checking your yellow pages under "building restoration & preservation" and/or "Masonry, repair & restoration".
I usually start though with the classifieds at traditional-building.com. Here is a first lead sheet for you for mortar matching - note several PA firms - if they match it - they can guide/advise on the supply of it: http://www.traditional-building.com/RTE ... tching.htm
You have one of the best resources in quakertown - less than 15 miles from you, now that's not too far is it?
Here is a nice article for you which includes the ASTM standards information that you might find useful:
Perpetual Student of the School of Hard Knocks: knows a little about a lot, yet knows a lot about little!