Shipping would likely kill you, but Rhodes are still being built by Stuart Marine in Maine. A call might get you some help on used parts on hand. There was a fleet of Rhodes 19s in San Francisco Bay years ago, parts and parts boats might be available. Also, keep in mind the ODay Mariner used the Rhodes 19 hull (usually centerboard version) and a simplified Rhodes 19 rig. Mariner booms will likely fit. Again, the major sources of parts are in the Northeast, so shipping is going to be a costly issue. But you can buy new booms from D&R Marine.
Fred W
Stuart Mariner 19 #4133 Sweet P