The zener diode is actually not necessary — the only diode you need is the one for the relay, which serves as a flywheel diode.
Any 5mm/5.08mm terminal block would fit (or you don’t really need a terminal block, you can just solder two wires onto the terminal block pins).
Relay: the one we use is HK23F-5V. Pretty much any relay would work fine — garage door systems actually use fairly low voltage (often 12VDC) while typical relays are rated for at least 110V, so the requirement on the relay is very low.