I might have found a replacement, but won't know until it (maybe) gets delivered. I called Jandy, who sent me to AO smith because they supposedly made the motor. They sold their electric motor business to another company, and two more phone transfers later I got a guy who works in the technical department of the third company that now makes the Jandy motors. Anywho, the guy said he had one sitting on his desk and would send it to me free. They don't do any sales there but he said it's a $0.15 part if you can find someone to sell them to you. His suggestion if I needed another one was to call all the pool stores/repair/builders and try to get one off of an older motor they have replaced.
However, in your situation since your motor is new I would be calling Pentair and raising **** until they sent me a cap.