Could anybody please tell me what kind of connectors these are? I've never seen them before. They connect to PA speakers like what they have in supermarket ceilings. And also, where can I get equipment that can hook up to those.
The round plug is a standard 2 pin DIN speaker connector used extensively on low end audio equipment in the 70's and 80's. The rectangular one looks like an old FM feeder/ antenna connector. IIRC AMP made something similar for a while and folks used to use em for 100V line applications
The DIN connectors you'll be able to get from pretty much any distributor, the other one I have no idea who even carries them now
The rectangler connector is a 300 ohm twin lead connector.
This is the best example I could find without diging for hours on the internet.
Yours looks like it was used as part of a wall plate set for 300 ohm twin lead many many years ago. You may never find these connectors any more.