Do you really mean collectors ? OR the exhaust hookups/reducers , the collectors are just that , the tapperd piece thats welded on most headers that gathers the primary tubes into one ( race stuff comes apart )reducers / exhauts hookups are the hree bolt flanged piece that reduce down to the exhaust you plan on using, and bolt or slip on to the collectors ( reason I am posting this is because I hear this term missused all the time , no biggie ) If its reducers you need , the common sizes are 3.5, 3. and 2.5 , Summit , Jegs have them the Flowtech brand is usually the least expensive, hope this helps
