I take it you are talking about the 83-84 ones. No one makes a kit like they do for the baby jeeps front axle disco, but I have read about people permanently locking it in mechanically over on IFSJA. I have one of these POS axles on my j10 and have not got around to messing with it yet.
I have talked to some people who have done this before, but never really go what they were saying. I have one that I am about to put in a YJ as well. Let me know if you figure out how to do this.
i have one of these axles in my bronco II. This problem was already taken care of when i bought it. The diff cover has a shift fork bolted to it that holds the collar in place that locks the two axles togather on the drivers side.
If you can find a long side shaft from another 80-92 waggy dana 44, you should be able to remove the vacuum disco stuff and replace it with a solid shaft...
iirc the disco axles dont have lockouts though... so you might want to get lockouts if your driving it on the road....