www.ebay.com
Honestly, that's really one of the cheapest places you can get one. I believe I paid $125 for a Mac o/r X pipe on there, and the H was about $10 more, strangely enough.
www.texasmustang.com sells them pretty cheap. You may have to call them for mac pipes their web page doesn't show they carry them, but their new cataloge I have shows they do.