Are you talking about the king that pulls behind a garden tractor, and looks like a wagon? Sears (sorry, but that's where I shop) has one on their website.. has 5 hp motor and runs $1m. I believe I've also seen them in Northern Tool catalogues.
I've got a Peco and love it! Here's a link to their site: http://www.lawnvac.com/
Mine attaches to the back of my tractor (JD 314), has a 4 hp B&S blower motor, and a bag that rests on the platform attached to the rear. Compact, no trailer tagging along, zipper bag for quick emptying. Bob