All CRs:
The French company TA is making modern replacement chainrings for 144 mm cranksets. The TA chainring appearance is very similar to Campy Super Record, and the rings are available as low as 41 teeth. The quality is good and the price is pretty reasonable, too!
I'm running TA 42x52 on my NR/SR equipped Mercian. The 52 ring does not have an anti-jam pin, but I haven't had any problems with overshifting. The rings have a special teeth cut which seems to make the chain run a bit smoother that average.
Andrew Gillis (Long Beach, CA)