There's actually another locker (auto locker) that should fit, but, it's pricey and you may have to import it yourself - it's the Brazilian made Kaiser locker and both front & rear are available to fit the 98~05 Grand Vitaras.
I don't know of anyone who has fitted these to a GV, a couple of guys I know have them on Pajeros and one on a Samurai, the Pajero owners are quite happy, the Samurai owner took it back out, if it could have fitted my car I would have installed it, just to see how it worked - it is an "auto" locker (or auto UN-locker), supposedly smoother and less intrusive in operation than the lock rights, but apparently they can still make for a twitchy noisy disengagement on a lighter vehicle.