Are you talking about hub assembly or the auto hubs for the 4wd?
If you're talking about the first one then I think the best alternative is the DynaTrac setup. However this will set you back a pretty penny and it was also on backorder when I checked. If you're running stock size tires they may not be worth it for you. If you're running larger then a 33" tire they're almost needed.
Hope this helps.