A 6mm pivot pin with holes for retaining rings at each end, can be made up by local marine stainless steel suppliers.
A much cheaper solution, that has held well for years on my old boat, is a simple galvanized 6 mm bolt and a wing nut. True, they start to rust after a year or two but they are so cheap that I can only buy them four in a package. You can buy twenty of those bolts and nuts against one Wayfarer standard stainless steel pin. Hence the SS pin gets cheaper after 40 years of use. 😉