Hi,
You can check internet on the site of FPI (Future Pipe Industries) or Ameron. Both are FRP suppliers. Note that sizes are manufacturer specific and based on a pressure rating.
ID of piping is standardized and considered being nominal, but the wall thickness and OD depends on the design pressure.
Best thing to do is contact one of these suppliers, because also fitting and flange types (end-connections) are very much depending on the application.
Regards.