Dear theside00;
To the best of my knowledge, Toyota never installed a front locking or a limited slip differential in one of their 4X4s, probably due to the threat of a massive lawsuit, however, since the front and rear carriers are identical, there's absolutely no reason why a person can't take an existing rear factory e-locker and install it in the front diff. This is a very popular upgrade down here although the factory e-lockers are getting sort of rare nowdays because everybody wants to lock their front diffs.
Your friend;
LAMAR