In reply to pebbles:
Petzl importer (so Lyon) would be the contact... officially though, I beleive you "can't" change the buckle...
My gal has however broken the end with the thin prongs now 2 times and got the replacement ok... Both have been due to missuse (forcing it to close, and not letting the magnet do its thing).
BTW. at least on mine, the buckle has stayed closed, provided there isn't any grime between the magnets... mine does seem to gather quite a bit of magnetic grime/sand there, so cleaning the magnets seems to help alot...