Try Gerhart Machinery in Litiz, PA. Their website says that they stock old and used parts for Murphy diesels.
Long time ATHS supporter, has a Mack event at their shop about the first week in October each year.
Phone:717-626-8544 or 1-800-786-8544
910 Brunnerville Rd.
PO Box 405
Lititz, PA 17543
This one was sitting on the floor of the shop in 2015 when ATHS had a stop at Roger Gerhart's on the post convention tour.
This one was in the yard behind the shop.