In my experience, the Shimano hubs are reliable and probably readily suited to your needs.

Someone in this thread posted a list of the drive ratios on available hubs, the Shimao Nexus 8 has the lowest drive ratio on it's lowest gear. These are also very efficient and robust drive systems, in my experience.

I don't know about availablity but those are made with a variety of OLD sizes and brake types. Get the correct one laced into a beefy rim by a bike shop. Multiple gearshift options as well with these hubs.