post a picture of it with the diameter of the unit and note any peculiarities in shape... now start with a google search "sailboat compass covers" and start looking for a compass similar to yours. There really aren't that many different kind. It will either be a pedestal mount, or a bulkhead mount. Smaller, open style, boats sometimes had their compasses mounted on brackets that allowed them to remove and store in a secure locker when not being used. Major brands you'll come across are Ritchie, Plastimo. The Plastimo Contest 101 and mini Contest are very common and have been offered a oem on production boats for many, many years. My 79 Catalina 27 came with a brass encased compass that was really beautiful but alas it lost the weather battle because one/all of the prev owners never covered it... it was left in place because, as I found out a few years back, it was near impossible to remove withour damaging the bulkhead. The replacement was the very fine, aforementioned Plastimo Contest 101. I have no idea how how old it is, I've owned the boat for 25 years and the unit looks perfect (light works and everything).... always covered by the plastic shield and the canvas bulkhead curtain that protects my teak washboards and other instruments mounted nearby.
If you've read this far, I am so sorry for the rambling, compass chat... but the deal is, for me.... I think all sailboats should have a really nice, large, good quality compass... I know.... we all use the chartplotter and gps..... but a really nice compass is SO, SO Salty... I just admire a well found boat with a beautiful professionally mounted compass.
Any of y'all have a beautiful compass and helm station they want to show off...... I'd love to see. I'm a tiller guy so I use the bulkhead style but it has an inclinometer and night light...and highly visible markings. But I'd like to see wheel stations that allow bearings to be taken, and relative bearings like take with a pelorus or a hand bearing compass. Okay.. done... sorry again for the ramble.