The masts in these were aluminum not carbon. Find a used light pole from a parking lot as they spec about the same as the originals.
The spec for light poles and for aluminum freestanding masts are not at all alike. While there were manufacturers of boats with aluminum masts who turned to light pole manufacturer's for their spars, those spars had an extremely different specification than the light poles. Aluminum spars are generally 6061-T6, which is a structural grade of aluminum that has good corrosion resistance. Aluminum freestanding spars were usually 6061-T8 or 6061-T9 aluminum, which are higher tempered versions of 6061-T6.
Light poles are typically 6063-T3 which is much lower strength (only 80% of 6061-T6), 'non-structural' product with only moderate corrosion resistance that is mostly used for architectural features in buildings.
The masts also typically had thicker walls than the light poles as well.
It may be possible to get a light pole manufacturer to construct a mast section out of 6061-T6 and temper it to T-6, or T-8. But it would probably be considerably more expensive than a stock light pole, and perhaps with the new boom and sail more expensive than the boat would be worth if retored and with the spars in place.
That does appear to be an Offshore 33. It would not sail worth a darn with only one stock mast no matter where you placed it. The Nonesuch was designed from scratch as a system to be catboat. The Offshore 33 was not; being designed from scratch to be cat ketch and so the stability, keel profile etc, does not lend itself to that adaptation to a catboat.