what do I need to get visa at HK airport or Luo hu?

If you are in a hurry, you can try to apply for urgent VOA when you arrive. However, I am afraid that your chance is not high because it requires the approval from the port where you enter. I think you should apply a L type from Chinese consulate in USA, which has jurisdiction over your city. Just tell that you need to get the L type as soon as possible. They might agree that you use rush service. You can get your L type on the same day you submit your application. Don't forget to submit your application before 11:00. Also, your wife needs to send you the invitation letter and a copy of her Chinese ID card.