Walmart sells sets of keyed-alike locks and a good drill bit can enlarge the clevis hole in a hitch pin. Keyed alike is available from other sources like Amazon where I asked for "padlocks keyed alike" and it gave me choices like 4, 6, 12 etc in the set, and types within set.
Maybe Tractor Supply for the pins.
W/out pix or instruction sheets, it's hard for me to picture where the pin needs to go. Simple spring clevis clips won't let you lose your towed vehicle. I think most of us who use locks want to prevent tampering, not even theft. They just don't want kids pulling pins as a prank, like to see what a fifth wheel looks like coming off the hitch with the landing gear retracted.
