There's two shops in Mayrhofen that do freestyle stuff, I can't remember what name but they are the same company, but all the hire shops do have freestyle skis. There's one next to the alpenhotel Kramerwirt. Hope this helps..
green room, do freestyle ski hire, i think its around 60-70 euros for the week and they seem like they've got some half decent stuff there, its next to funkys bar about 200m off the main street.