I can catch reshiran and zekrom?

Yes, you can catch Reshiram or Zekrom depending oN which version of the game you have. Sorry for Spoilers, but When you have completed the main storyline, you can Battle N in the Ruins of his Castle. He has 1 Pokemon. A level 70 Reshiram/Zekrom, (Again, depending on the game you have) Once you have defeated his Pokemon, he gives you the Light/Dark Stone. You can then travel to the top of Dragonspiral Tower and select "USE" at the Light/Dark Stone. You can then catch a Level 70 Reshiram or Zekrom.
Hope this Helps!
PS: You caN Battle N afer that, he has a 6 Pokemon Team depending on the season that it is. You can battle N every season.

You can only catch Reshiram in Pokemon White 2, not Zekrom. Zekrom is exclusive to to Pokemon Black 2. However, you can still obtain a Zekrom by Trade or an Action Replay Code.

After you complete the maiN storyline, you can find N in his castle's ruins. You can get to his castle's ruins by follwing the Zoroark in Victory Road. If you defeat N, he will give you the White Stone. If you take this stone to Dragonspiral Tower, you will have the chance to battle/catch Reshiram.

Hope this helps!

You can get Reshiram (Pokemon White 2) or Zekrom (PokemoN Black 2) by defeating N. You can get Reshiram/Zekrom by finishing the main story. Then, you'll start in Aspertia. When you go out of your house, Hugh (your rival) and his sister will tell you something about Zoroark in the Victory Road. So head to the Victory Road. If you see Zoroark, follow him. Then when you are already deep inside the cave in Victory Road, you'll see N and his castle. Go inside and you'll be welcomed by N. He'll ask you if you can lead him to the deepest part of the castle. Say yes. Then once you're there, he'll ask you to fight him. Say yes.

Reshiram
L.V. 70

Fusion Flare
Extrasensory
Imprison
Dragon Pulse

OR

Zekrom
L.V. 70

Fusion Bolt
--FORGOT--
Imprison
Dragon Claw

You can catch victini in liberty island but you will need garden pass to reach victini