I'm wondering since you asked specifically for C-Record chainrings you want the retainer pin in the right place (eg; aligned with the crank arm) and/or the knurled nut for the hidden bolt?

If so, nobody is making them (afaik) so hit up your favourite used parts dealers. How many teeth are you after? Some sizes seem more available than others.

If not, then TA Specialties as mentioned above is your best bet. Still might be worth checking the second hand market as the older TA rings looked pretty similar to the Campy jobs.

If you don't have a knurled nut you can use the sleeved part of a track nut with Loc-tite.