The basic breakaway coupling was just a sleeve of aluminum
tubing with a relief cut to create the breakaway feature. The rudder
itself was a foam filled FRP affair with an aluminum
shaft. If you can source the right sized tubing and and get the dimensions, like how deep to make the relief cut on the coupling needs to be, and overall size of the rudder, should be easy to fabricate the whole affair. Would be a lot easier to see if you can find one that's been laying around in someones garage, though.
Sorry, don't have any dimensions as my Aries has long since sailed off into the sunset on my old boat. The Aries is a great vane with the best windvane
adjusting system. Probably would be a good idea to disassemble the gear
and reassemble with lanolin. The insulating properties of lanolin will make it easy to service
in the future should the need arise.