Zip Products is where I ordered my handle. The website is www.hiperformancemustang.com Also I believe Dallas Mustang and Partshopper carry it. Expect to pay around $25 to $30 for it. I have one for my Pro 5.0 and love it.
Check mustangtuning.com. If Chris or Pete don't have it listed on the site, chances are, they probably can get it and hook you up. They'll take good care of you.
Dammit! I PM'd you about trading me. I want a pro50 handle. Should've read the whole thing before I PM'd you. =/ If anyone else wants a Triax Handle for a pro50, I'll trade!