I'm currently working on a handful of projects and under the current market am having a little trouble finding a few parts at a decent price.  The local gun show was of no help whatsoever and the only gun store in the region deals only in hunting-related materiel.  I was told this was one of the best resources on the web for information.  Any help would be appreciated.

Parts in order of importance are :

single rail (top) low profile gas block with bayonet lug
KAC two-stage trigger (screw adjustable, not swappable springs)
MagPul MIAD AR15 (basic) pistol grip (CR123 core preferred)
buttstock pad for aluminum 4-position stock (widest dimensions 4-1/4" x 1-7/8")

In the not-so-distant future :

KAC 600m flip-up rear sight (4)
KAC front sight post push-button sling mount combo (4)
AR15 Crane-type telestock with tube, carbine buffer, and spring (5)
push-button sling mount (KAC or other) for Crane stock (5)
Tenebraex polarizer for Springfield Armory Gov. 5.56mm 4-14x scope
replacement KAC panel spring clips (black) P/N 93133

EE board.

+1 on the EE.

But check out the Dealers in the Industry Forum as well.
I've bought from Denny's Guns, Bushmaster, RB Precision, Eagle Firearms & Leagal Transfers, just  to name a few, all with great service and good products.

CD

For your KAC needs, Operation Parts is one of the faster and more inexpensive KAC suppliers.

Added a link - Operation Parts KAC Equipment