How do you get a Axew egg in Pokemon black?

Answer 1

You could catch fraxure (both have to be opposite genders) evolve both and take them to the Pokemon day care and there you go! one axew egg.

You could get a ditto ( you can get one in both black and white) and have one fraxure and that them to the day care center!

Or you can catch Axew in Mistralton Cave and breed them using methods mentioned above.

My personal view is using a ditto is far easiest as you dont have to worry about genders of axew / fraxure etc, and you can just keep a ditto in daycare all the time.