The real "demo" knife from the early 1960's is such a rare bird you may never find one for sale. If you do be prepared to pay over $2000.00 for it. It was made for the Special Forces during Vietnam. It was made from non-magnetic and non sparking materials, not steel. The copper blade dulled very quickly. It was never approved for issue.
The knife commonly refered to as the "demo" knife today is nothing more then the all stainless steel U.S. marked 4 bladed scout type utility knife. Properly known as the mil-k-818c. These knives are issued in demolition kits hence the name. The knife with two blades one of which is a locking screwdriver is actually a TL-29. Is is a Signal Corps / electrician knife hence the TL, Tool, Lineman, number 29. It is not a demo knife, although it could be used for one the blades make an improper size hole for the blasting cap. The original demo knife and the mil-k-818c using the awl blade do a nice job of cap setting.
As for the original question, the knife you are probably looking for is made currently by Camillus with the model number of 1706 I believe. Around $15.00 should buy you a brand new one. The main cutting blades have been dated since 1957. If your friend is looking for a specific date the prices could go considerably higher.
Frank Trzaska