Where can I get data on CPI? Like number of customers served. Size of service area. Stock symbol on NYSE. Lots of things on the CPI web page but they don't answer these questions.

CPI isn't a publicly traded company so no stock symbol. They are owned by their members and are a cooperative. This page says all of the other things you are looking for. https://www.cpi.coop/about-cpi/

If you go to their website and click on the ABOUT CPI tab instead of clicking on one of the drop downs on that tab you should find some of that information.