As Candace said it's probably a Japanese model. "MOST" as a matter of fact all the Japanese machines I've got and seen take a Class 15 bobbin. Sew-Classic.com has them. There is two basic ones the machines take depending on weather the bobbin faces left or towards you. Once you get the machine home ... yes we are a bunch of enablers ... and tell us that I can tell you which bobbin case you'll need.
Go buy it ...
Joe