You can't get it from a 2005. I think in 2009 there is a mystical rare 4th gen trail edition that had one. Probably the precurser to the 5th gen trail edition.
You also can't just pop it in.
The diff housing needs some little modifications, you also need to have a way to actuate it since it's not part of the ECU programing, and you need to make sure the diff is the same ratio as the front.
You need to search for some write ups to see if it's something you can do if you do it yourself or if you can find a mechanic who will get into modifying stuff for you. If not a buddy who can do it if you can't alone. But I think it can be done. Seen it on older generations. Not on 4th gens. And I haven't looked it up here to see if anyone did yet ona 4th gen.
FJ Cruisers, some 3rd Gen 4runners, and some Tacoma have them. Not sure if the axle width is the same. But the 3rds do fit with some grinding down of the diff housing. If one of those is the same width just replacing the whole axle might be an easy DIY way.
New these are expensive. Used, I seen these go for 500$ for the 3rds with elocker.