Kathieo - I've found mine in two spots....I always check the sewing section of any thrift store, value village etc. when I'm in them and scored a few that way. Call your local repair shops that take trade in machines - some keep spare parts from the machines they junk and the attachment box yields some bobbins that way. Just a couple of options that worked for me. If you are unsure if your bobbin will fit carry one of the ones that work in your purse to size them up - I can do this when they are in clear bags. Some shops have bundled all sizes of bobbins together but if you ask sometimes they will open the bag and extract the ones you need. Budster

Check this link,it's a legitimate sewing machine and accessory link.

http://www.sewusa.com/Threading_Diagrams/Threading_Pages/Singer_Sewing_Machine_Threading/singer_640_threading_diagram.htm

Kathi