w7sue,
Two places to look for a friction drive wheel:
Thayer Rags Parts {
http://thayerrags.com/ }
Sew-Classic {
http://www.shop.sew-classic.com/ }
You'll need to know the motor shaft diameter: 1/4", 9/32" or what ever, and the outside diameter of the drive wheel if you have it.
If the motor is spring loaded you'll have a bit of flexibility, but if not then you kind of have to be on with it.
Joe