I noticed that there were not any lockable gate latches, so I decided to create and upload one.

Key Features: Lockable Strong Hidden screws (Screw hole covers included). Secure screws when locked, they can't be removed. Reinforced latch pin (2" deck screw threads into the center of the pin). Sun-proof, use "MakersGeek's Raptor PLA" (safe to 500 degrees Fahrenheit). Parametric Openscad file (also usable on OpenJscad.org). Adjust overal length, receiver length, pin radius, and wall thickness. Screw hole size is tied to wall thickness. Default Facet Number is set to 36 for quick rendering. Printed file was rendered at a facet number of 360.