So now I have
at least one cable and can use that to make a 2nd if need be.
You could instead
make an adapter to go from the 9-pin to the 15-pin, then
just continue using standard 15-pin to 15-pin cables, and just plug on the
adapter
when needed.
Or,
once the pinout is confirmed,
open the case, and replace the DE9 with an HD15 connector.