If I remember correctly, the power steering belt tensioner was on the bracket with the p/s pump. The bracket had a slot in it. The tensioner was simple device; it had a pulley wheel for the belt to ride on, and the wheel was attached to a metal piece that was adjusted up and down the slot by turning a long threaded bolt. Up put more tension on the belt, down relieved tension.
I'm not sure if they are interchangeable between years. I know the '84 and '85 GSL-SE engines were fuel injected like the '86 and up engines, but I'm not sure if the brackets for the external components were laid out the same.
As far as getting a new one, I'd check the for sale section of this forum. If nobody is parting out a car like yours, post a thread asking for the parts you need and see if you get any offers.
Now why the **** do I have to press 1 for English?