To my knowledge, Brownells factory parts availablity is only DPMS and Colt, and you sure don't want to pay Colt's spare parts prices. Bushie's parts are listed on their web site, and some of the dealers who list on our EE section also stock Bushie pieces.
For you "DPMS is wonderful" guys I can only assume that you've never seen a well finished AR.
Don't get me wrong. There are plenty of DPMS parts at my house-----and nearly every one of them has had work done on it by me to make it acceptable for use in one of my ARs.
Examples:
The black anodised receiver extensions from DPMS come with only the base shiny black anodising, and lack the final dull finish coat that Colt, Bushie, Stag, and most everyone else applies. Ditto with the trigger guards and mag release buttons. OK; I'll take the time to apply the final coat, if getting the DPMS piece saves me a few bucks.
Front hinge and rear securing pins consistently come with circular tool marks on trhe head and little bumps on the left side. OK, I can "finish the Finishing" that DPMS's contractor didn't bother with, and re park the piece.
Hammers and triggers? My polishing stones will get the tool marks off the bearing surfaces and smooth up the pull.
Buffers? OK, so the face of the DPMS ones in my rifles show more wear and finish chipping after 2-300 rounds than the Colt piece in my 37 year old Colt SP1 does after multiple thounsands of rounds fired. They work OK and I'll live w/the chipped appearance every time I open the action.
In sum---if you believe that DPMS sells well finished spares, your tolerence for sloppiness is much higher than mine. I'll buy 'em if the price is right, but Iwon't put the bulk of them into/onto an AR of mine until their finish matches my own standards.