You can use any 4" inlet filter you find. A lot of people swear by the AEM dryflo. You can buy the $15 filters from AutoZone or eBay too if you trust them. I do not.
1999 GTP Coupe ------ Comp Cam 76-802-9, 2.7" pulley, S2IC, N*, FWI, SD Headers, DHP Tune, Built trans (single 3.29s, 300m), Magnaflow Catback, 60#injectors, E85, MT ET Street DR's, Fbody brakes, PRJ pump/rails. 302whp/328ft-lbs.......12.41@110mph