CV Unlimited makes some hd cv's:
I've honestly only seen a few cv failures in person on Tacomas, even with larger tires, lockers, and relatively hard wheeling. Most of the failures I've seen were due to liberal use of the skinny pedal, when a more conservative approach would have accomplished the same thing.
Certainly the front locker will stress the front end components more but it sounds like something else is going on if he has the same failure every time.
2002 Jeep Liberty Limited 4x4
OME heavy springs
Bilstein front struts and rear shocks
Yokohama Geolander AT-S 245 75r16