I'm relatively new to 1/12 myself so you may want to send them an email to confirm but you probably want something like this:
http://www.lefthander-rc.com/catalog/product_info.php?cPath=28&products_id=787

Alternatively if the axle diameter and offsets are the same no reason you couldn't use an associated or other axle available at your local hobby shop. My understanding is that most if not all 1/12 cars use a standard axle diameter. Offsets I'm not so sure about but it might be something you could fix with shims. Hope that helps.