Unless you have your heart set on Colt specifically, I think this is a perfectly acceptable alternative:
http://www.bravocompanyusa.com/AR-15...le%20ar-15.htm
Bravo Company has great kit and you could do far worse with their parts. But if you're looking for Colt specifically to match the brand, they sometimes pop up in the E&E here.
As for the stock, depends on what kind you are looking for.
Yes, the Lula mag loaders work with just about any AR pattern mag. I've used them on Magpul, Lancer, Elanders, H&K steel, Troy and USGI pattern aluminum. No problems with any of them.
Works fine with 55 grain. 52-77 grain is the best range for ammo choices.