24" bike or 24" wheel? Or is it both? I've got a 24" wheel (coaster brake) but it is on a wide rim (for a BMX). But I'm not from philly, so it would need to be mailed. You would likely want to rebuild the wheel anyway, so your best bet might just be to find a hub and spokes and build from scratch.

As for low-powered ratio in a hilly area, I'd suggest multi-speeds. If that isn't cool enough, consider the low profile potential of internal gears. I've got a few buckets full of Sturmey Archers hubs for dirt cheap.