Reading up on Bulbapedia, I have to wait till Mistralton cave to get an Aron in BW2? D:
I might actually just trade it over tbh. Catching an Aron at around lv 27-ish and breeding for some egg moves in the middle of the game, and train the new Aron up to have in my team?
...I might prepare an Aron with egg moves around lv 25-ish, and trade it to BW2 when I catch one there. That would be legit-ish.