Is it circular with two cylindrical prongs in the jack? This was semi-common on office equipment in the 40's/50's/60's. I don't know where to buy them new, but keep an eye open for other office equipment from that era. If you can find similar shape/size contacts in any of the "modern" plug/receptacle lines, one common technique is to crimp the contacts onto wires and then mold (using epoxy, hard silicone/RTV, etc.) a new plug around them. For just dinking around many of us have been known to use alligator clips :-). Tim.