I have a Zekrom. Caught it yesterday. Not sure about its nature or anything. If you want anything specific, I'm afraid there's only a small chance it'll have the right nature for you. Its level is still in the 40s, can't be bothered to check which exact level it is right now.
If you have any event Pokémon I don't have yet and you're willing to trade it for a Zekrom, I'm honestly willing to trade all my Pokémon from White to Black, play through the game again (will take like two days) and catch a Zekrom with your preferred nature.
I'm really only looking for a legit (event, of course) Celebi, Japanese HG/SS UT Latios (there was a Wi-Fi event for this one a while ago, I got the Latias, but stopped playing Pokémon before I got around to getting Latios as well, I'm not sure if HG and SS are the only games it was available on, pretty sure it was though), Deoxys or Arceus.