I always go through my bucket of car seatbelts before I fit one. the ones with a button that moves parallel to he belt/clip unit will open when under better than the other type. . In WA wreckers may sell the strap but not the buckle. ( so I was told by a wrecker). Try a metal scrap yard ,they dont care( so I was told by a scrappy)
I just look out for wrecks in the bush, but then I live in Kalgoorlie.
Many years ago I saw a Landyacht that had a plastic buckle from a camping store that had the 2 sided squeeze set up to undo. I thought that was great and got one myself , but 2 years later it snapped when I REALLLLLLLy needed it . yacht went by the name of Wildfire




the 3 seater yacht has a 3 point harness for the passengers, and lap for the pilot. VINDI 4 point with extra padding. all the other yachts just a lapbelt.
Bill talked about the EUropeans and no belts, IN Rada Tilly I talked to the guys from AIRTRACK about belts and explained that in France there are so many rules and laws that asking (telling ) sailors that they should wear a belt would get you told to p*ss off. and that was the reason they dont wear belts