What else, barring cam and some supercharger pulleys, are toothed belts used on?

I need 2 pulleys, one about 3 times the size of another, ie a 3:1 ratio if ran off a single belt, but cant think where i can find 2 of such different sizes, esp as want them no bigger than cam pulleys at best really.

Any ideas? Id guess thatd cost a lot to get custom made, wouldnt it?