You can go to Mistralation cave and wonder around until you encounter a wild Axew. Do the usually to catch it. Since it can be caught like any other pokemon. Another way you can get an Axew is by using Global Trade at a Pokemon Center. You need to register first btw at the planet thing. Talk to the lady on the very right. Select Global Trade and save the game. Easiest way to do it is GTS. When you get to the tower, select Deposit pokemon or the next one. With Deposit you can put in pokemon you wanna offer and when someone finds the pokemon your offering, and they have the same pokemon your seeking. They will trade with you if they want to. If you select the next feature, you can browse for people who are offering pokemon. You can select what pokemon you want, what gender, what level, and where that person is. To see what level or what the pokemon is, look at the top screen. You can see what pokemon they are, what level, what gender, who there real trainer was, and what there nickname is. On the bottom screen you can see what the person wants and who you are selecting.
Hope this helps :)