IF anything is still available, it'll be a header made by MAC and found on Ebay. You might do a statewide criagslist search for an aftermarket header for one that someone is trying to sell. I will warn it aint gonna be fast unless you rip the head off, find a set of cams, port it and do a quality header, and flat slide carbys. BUT then it'll friggin scream for what it is. Might also find a GS400 specific forum.