InB4 people who understand ITAR regulations...
You'll probably be told by people more knowledgable than I that bringing AR parts across the border is a recipe for trouble, although the misinformation seems to continually persist that such actions are legal because "I wasn't caught".
It makes relatively little commercial sense for a company to market a complete (sans lower) kit for building an AR, as most builders have very specific specifications that they want to build a rifle to. Depending on what kind of setup you want, you may require very different parts (particularly when choosing handguard parts). Take 30 minutes to put together a list of what you need, and then purchase it. That's half the fun. As previously stated, TNA usually has everything in stock that you'd need for building an AR. A parts diagram is a handy reference for making sure your shopping cart has everything you need.
If I were to put together a list off the top of my head, I'd say you need a:
LPK (lower parts kit, make sure it includes a trigger)
Grip w. mounting hardware
Magazine
Buffer tube
Bufffer spring
Buffer (Probably H1 or H2, but depends on your barrel length)
Castle nut
Stock
BCG (bolt carrier group)
Upper receiver
Barrel (which may or may not have a gas block)
Gas Block
Gas tube
Barrel Nut
Handguard cap (if using A2 front sight barrel)
Handguard set (if using A2 front sight barrel)
Free-floating handguard (if not using an A2 front sight barrel; this may require a specific barrel nut setup and requires research)
Forward assist assembly (may be included with upper)
Dust cover assembly (may be included with upper)
Charging handle
Sights/optics of choice
Grease for buffer tube and barrel threads
I think that's most of them... been a while since I built mine