My Nervar Star 128 bcd cranks take a standard 22 mm crank tool. There are rings out there, though sizes other than 40, 42, 52 and 54T may require going to French eBay like I just did in pursuit of a 44T ring. They are really nice overlooked cranks.
In a pinch you can modify 130 bcd c’rings to fit the 128 bcd Nervar by dremeling the holes inward 1 mm each. I’ve done it and it works and doesn’t look too bad.
if that turns out to be a full 531 Gran Sport and it fits you have a fun project to build. I keep waiting for a deal on a 23.5-in to come along at the right time.