How low of a low do you want? Are you willing to have a wheel built for this?

If 43.6 or so is low enough, you could build a wheel around a shimano Capreo hub and its 9-26 cluster.

43 up front would get you within 1.1 gear inches of a 53x11.

Your low would be 43.6 compared to 39.6 of a road standard 39x26.