You are unlikely to find one with an identical cam but you may be able to find one that has a similar sized shaft so you can use your own cam. They are called Cam Locks or sometimes cabinet locks,and they should be available in hardware shops. The important measurements are the diameter of the screwed barrel that goes through the hole in the front box and the length of the barrel so that the cam (whatever you use), engages. If your lock is the same as mine the diameter of the barrel is 3/4" (19mm) the length of the barrel from underside of the "cap" is approximately 1/2" (13mm) + the length of the square threaded bit that holds the cam which is about 8mm. The squared end is 15mm square. The overall length of the cam is 50mm but it is "cranked which may be the stumbling block to finding an exact replacement. When I replaced mine I found a lock that matched these dimensions except for the size of the squared end and made up my own cam to suit from a scrap of metal, drilled the hole and squared it off with a file. Hope this help
take the lock into any good locksmiths shop for replacement parts, a lot cheaper than any caravan dealer.
good advice from Alan above (lived in T Atatu for 2 years 1964 to 65)
I can guarantee you wouldn't recognise Te Atatu now alpiner or Auckland
Unlike the door lock, the lock from the front box is not dismantle-able so it's definitely a whole replacement lock. The door lock is simplicity itself to cut your own key for.