I found these on eBay:
http://www.ebay.ca/itm/272156704955
Cams are often difficult to find for specific machines. In your situation, I would be tempted to snatch these up.
Edit: Oops! That listing has ended. But at least you can see what they look like and perhaps do additional searches using the Viking designation for this machine.
Edit 2: I would save a search on eBay so you get emailed if something like this comes up. You need to create an eBay ID in order to save a search, but it's pretty easy to do.