Converter?

well i've been trying to do my research and get ready to do some engine work on the alero but i'm still missing a few pieces that i haven't found which one happens to be a converter. i'm just wondering if anyone knows where to get a good high flow cat at for a good reasonable price? i saw the post about the s&s headers and i think that is the route i'm going but they are out of stock right now. i'm going to try and wait and order it all at the same time or at least the components that go together such as exhaust, intake, throttle body, internals, and what not. if anyone knows of good deals on any of this please let me know. thanks