First, I would try taking out the screw and taking it to a good hardware store to see if they have a matching one and then rewiring with the original plug.
If you have a local sewing repair place, take it in and see if they have a cordset to match.
If that doesn't work, it looks like a Necchi/Pfaff plug like this one:
http://www.shop.sew-classic.com/Cord...lead-SCE32.htm
You could measure the distance between the holes in the plug (center to center to center) and write to Jenny at SewClassic to see if it looks like it would match. I think she also accepts returns (although you would have shipping charges).
Good luck.