The O'DAY 20 came out in 1973, so if yours is a 20 she would be 1973 or later. D&R has the spreaders, but Rudy will need to know which type your boat has, the model year usually is an indication. DWYER Spars in Connecticut is another source, but D&R will supply the exact length without needing the old one to measure.
I'll add a picture of the 1973 O'DAY 20 for reference, you mention "2+2" so I wonder if you actually have a 19' MARINER instead of a 20? I'll add a picture of one of those (actually 2, because O'DAY phased in a different deck design on the Mariner during 1972).
The Mariner rig spreaders were pretty much the same type for all model years, but Rudy can advise.