Sterrn,
I have an '87 'S' and got a K&N air filter from Zims in Dallas. You can order from them online
http://www.***********/
The air filters are under the maintenance category. I just checked and the price on them was $35.95. I get all of my parts there and really like the guys there. Anyway hope this helps. Oh and remember, you have to oil the filter before you put it in.