I am guessing you ordered an AP4 model (M4gery) from DPMS. Nice rifle. Got mine back in March 07. Love it. Not a problem ever with it. But even back then, I sat through a 2 month wait. Of course, when the order was called in by my FFL they were told it would be in in about 2 weeks. I made a few calls to DPMS myself after a month had went by. And finally someone there lit a fire. Other than that wait, my experience with DPMS has been stellar. I have ordered several parts and accessories from them and have had nothing but a great experience.
That said, 6 months is too long to wait. You may call them and explain to them that you were wanting the rifle sooner and that a 6 month wait was not expected when you ordered and see if they can wave the restock fee... since they arent really restocking anything to begin with. Keep us posted on that one. Might just cause me to look for other sources in the future if they try to hold to that practice. And just curious, did YOU order the rifle or did you have a FFL make the call for you?
Several site partners on here can supply you with what you are looking for. As stated, gunshows are always good, Hell, there was a distributor in Shotgun News that had DPMS's pretty cheap as well. Sources are there, just gotta look for em.