Aussie Locker provides a front mechanical locker. There are the perennial and expensive ARB air lockers for the front, also. I would suggest finding an air locker from a Mitsubishi Pajero / Montero / Shogun with 9.5" ring gear for the rear, or a 9.0" ring gear unit from a Challenger / Pajero Sport / Montero Sport....thus matching whichever rear axle you have.

Cheers,
Russell