Hi Michael'

1. You need wheels with a 622mm Bead Seat Diameter (BSD). These are also known as 700c, 29 inch, 28 inch - depending on where you are, and what the wheels are intended for.
2. A direct replacement is a 5 to 7 speed freewheel rear wheel with 126mm OLD. In modern terminology, your bike is a six speed or 2 x 6 (=12).

You have a beautiful example of a VERY inexpensive bike, not desirable to most collectors.

Why do you want spare wheels?