Ok. The most popular kit manufacturers in the states is
www.carkitinc.com their Mercy-2 is the LP640 version and are a legitimate company in Alabama.
Also, Robslp640 makes LP640 and now claims to be ready to sell Reventon bodies too. Do some research on this guy as some people have had issues with him delivering product after he's been paid. Also some people have been fine dealing with him too. However this is only what i've observed and i have no personal experience with him myself. He has several vids on youtube where he leaves his number and i think he has a webpage too but don't know the address. He is located in Arizona.
Also, IKR or Italianknightrider on this board may be ready to sell Aventador bodies. But you should PM him to get better details and possibly pics. He is located in Texas i believe.
One last thing. Never send any money without seeing things in person first and try if you can to pick up in person. Many a scammer in this kit car world. Plus, the word "kit" is a generic term when it comes to lambos. All you get is the body shell and some interior pieces and you have to fab everything else. That's where these great message boards come in. Good luck