Once you identify the type and size of your headset, you can find a vintage style fork.
If your headset it 1" threaded, most springers (cantilever style) should fit.
If your headset is 1-1/8" threadless, you can use one of the Monarch style springers from EBay (check with the seller). You could also use a dual crown fork like a Roxshox boxer or Marzocchi shiver.
If you have a 1" threadless headset, you can use a Girvin fork.
Search on the above forks on EBay to see what they look like.