The problem is the leather - at 57" you're pushing the limit of the hides ('cos you have to add about another 3"-4" for the buckle turn), although you can get longer ones out of some butts. Width isn't so much of a problem, although many belts are conditioned by the available buckles.

Weaver Leather of Mount Hope, Ohio, does cut up hides into mail order straps for belts and some of them are pretty long. You could give them a call. If you've got somebody who could make up the strap into a belt, you'd be well away.