He probably cast it himself. You can actually cast aluminum pretty easily, with a little training and a hot fire!
Theres a guy on the Marlin Crawler board (Toyota Rockcrawling forum) that cast his own Supercharger nose cone for a Nissan diesel engine. He did it in his driveway with a vacuum cleaner supercharged fire...
It would actually be easier to build one out of sheet aluminum and weld it together though. On my truck, I ended up welding an extension to an ATS intake hat to hook up my IC plumbing...
Ryan