Hello DAG Stew,
Check for a brand name on the ports or the frames. Might be Beckson. If they are Beckson just search Beckson Ports and buy from the company or check this site. Size information will include "glass" size (perhaps lite size), cut out size, and overall size (includes the frame). Gaskets, screens, "glass" are also available seperately if you only need parts. If you only buy parts remove the old ports and recaulk the frames anyway. Use care removing them and save the parts until the repair is complete.
Best Wishes
NOTE: I did edit my original post. I had written "Bomar" by mistake for the brand name.