How can I get the event shiny legendary dogs and a celebi for your Black and White without cheating

There's really no way to. If you don't have the event pokemon on one of your older games, the event is basically unaccessable. If you are trying to catch Zoroark, an alternate method is to go to the building in Castelia City with the 2 characters; a girl and a quiet boy, where you can be shown a picture of Zorua, allowing you to then obtain a Zorua from GTS. Then evolve it at level 30. I hope this helped! :D