The 115 bobbin case shares with a 20U industrial machine. The bobbin cases are trivial to find.
Try these links:
http://www.quiltingboard.com/vintage...e-t216990.html
http://www.quiltingboard.com/vintage...n-t240338.html
http://www.quiltingboard.com/vintage...l-t235346.html
My 115 is a "Wings", and I've used it for a couple of small projects but haven't bonded with it. I can't say why though.