Hi Big Red,
Most spokes are either 14 ga. [standard bicycle], 12 ga. are .105", and 11 ga. are .120".
All new edition Whizzer have 12 ga. spokes and are laced differently than vintage wheels. The spokes are shorter on the new edition wheels because of the lace pattern. Vintage 26" wheels use 10 5/8" long spokes [new edition are 10 1/4" long].
10 1/4 is the length.
14 ga. stock bicycle
12 ga. stock for most vintage and new edition Whizzer wheels.
11 ga. used on many vintage Whizzer wheels and Worksman.
Larger spokes [11 ga] will not fit the Whizzer sheeve cips correctly and will cut spokes over time. Clips can easily be modified to fit the larger 11 ga spokes.
When replacing rear rim, please note........................... the rear hub is a very, very, very poor unit and will most likely destruct [I have at least 30 defective Whizzer hubs in a box].
The rear hub has pressed on spoke flanges and they move to center under stress. A rear hub with loose spoke flanges makes riding at 35 MPH impossible [lol].
Use a Shimato, Hi-Stop, or any vintage coaster brake hub [Bendix, New Departure, Morrow, etc].
Worksman is most likely the best choice [I have several in my collection with Worksman wheels], however take a look at "Husky" wheels, as they are much less expesive, and still well made.
I know money is tight in these dfficult times, however spending extra for a good wheel is a must for safety. Also consider the amount of work required to remove and repair a rear wheel. I always make sure the rear wheel is way above stock, as it is the most difficult part of the motorbike to service. I always use thorn resistant tubes to avoid any service other than replacing the tire when worn out.
I don't know about a spoke chart, but there is plently of information on the internet about spokes, lace patterns, and HD wheels.
Have fun,