If I were looking for used axles, the first places I would look would be Craigslist and junkyards. If that doesn't work, you may want to try your local offroad shops. They sometimes have take-offs from builds for sale.[/QU
I have been doing all the above and thought I would add one more place to get the word out. Off road shops are very limited in my area.
If shipping isn't an issue, Burnsville Offroad usually has take-off D44's in stock.
http://burnsvilleoffroad.com/posts/category/parts-for-sale/
Hope that helps. Good luck with the build.
I'm not sure if this guy is just selling the ring and pinion or the whole assembly:
http://www.nmoffroad.com/forumvb/showthread.php?t=15990