it's difficult to find parts so far. I would like something in 14.5" or 16". any leads on where I can find complete uppers?
I would like something with a rail for optics and grip upfront.

This has been covered many times but YHM sells them still I think. I've only used one of their barrels but other than that no experience. Sota arms they are cheap and will shear bolts(I don't no this from experience only read horror stories) and cason engineering sells quality product. They are the ones making the high quality 7.62 bolt being talked about a lot. I no their upper is billet and comes standard with a MI gen 2 rail and black whole weaponry barrel and a titanium compensator.  
Maybe try building your own upper?

SOTA arms...their build quality is great and im very happy with my upper!

http://sotaarms.com/component/jshopping/category/view/5

I got my barrel Here and it's still on sale now, my only problems with it are it's an HBAR and I'm not crazy about the 5/8x24 thread pitch. Normally I go cheap on muzzle devices and I would rather drill a cheaper 5.56 one compared to this thread. Overall though great barrel, my complaints are probably dumb problems to everyone else.

*edit, I thought you were building and not just buying*

I have been looking at a 7.62 build for my next one....   I have the parts together to finish my .300 build this weekend.    I ordered one of these:

Flash Hider - 5/8

My barrel is SS, so I thought that it might look cool.

New to the forum , been lurking a while though.

I don't know about buying a complete upper, but I just built my second x39 upper with YHM and DPMS parts.  YHM still sells chrome lined 16" barrels and I used their parts for everything but the receiver, they had none and had no idea when they'd get em.  I used a DPMS slick side receiver and a MGI bolt and firing pin to finish out.  Had to do some dremeling on the feed ramps to match the barrel and receiver together, did a function run and she runs flawlessly. BTW Midway has the MGI bolt/firing pin on clearance for $79.

If ypu are open to building the upper, Midway sells a 16" midlength barrel that comes with a bolt.