For AUG A3 BB you need these two parts. Not apply to NATO stock version.
For extending your AUG A3 OLA to 30" you need this part.
2. or you can find a 20" or 24" US made AUG barrel. http://www.pjs-steyraug.com/augusrparts.html
Finally, buy some wood stick and make your own 10/30 AUG mags.