Dave and other interested listmembers. It was stated on the list that a 13 tooth cog was not available for the "Pro Compe" or "8.8.8" bodies. Well I have a SunTour "Perfect" freewheel, which I think is the same as the "Pro Compe or 8.8.8." body, and it has a 13 tooth small cog.
I'm not a SunTour freewheel body expert, so you may want to query the list for a confirmation in the ProCompe/Perfect compatibility. If the bodies are the same, then you may have some luck finding a 13 tooth cog, as previously stated, I have one on a "Perfect" bodied freewheel.
Best of luck with your search!
Regards,
Kevin Kruger - Grantville, PA