I think most early O'DAYs used ZEPHYR spars, Zephyr is still around, and located in Wareham, MA you could order a new mast from them, or just the extrusion. Given the age of the mast, I'd lean towards replacing the whole thing, aluminum fittings age and weaken, they also fuse to the extrusion after a while. Any local rigger/sparmaker can repair/replace most masts, I suspect most actually use the same extrusions (and maybe fittings). Zephyr does own the dies used to extrude their spars..... but really, Dwyer spars will be darn close! (Zephyr actually buys a few of their fittings from Dwyer instead of getting them made custom).
Zephyr is part of Cape Cod Shipbuilding,
www.capecodshipbuilding.com
I'd be pretty sure that the Osprey used a Zephyr #1 extrusion, That should be similar to a Dwyer #275 section. My Dad used to have an old Beetle FALCON (the Osprey was a clone of the Falcon, and actually both were built by Marscot Plastics when Osprey was introduced) and the original mast was a Zephyr size #1, which is exactly the same as a Dwyer #275.