Well, there are tons of batteries to choose from out there in all sorts of price ranges and chemistries, its not a case of fitting one inside a hub but rather of making/finding the hub to contain the battery itself. I don't know of any way to easily go about doing that, all I can suggest really is trying to watch ebay in case one of these tidal force systems or even one of the wheels comes up for bidding. Someone else might have a better suggestion.

I don't really know much about the Tidal Force bikes, but the battery hub was an interesting angle. Having the weight right on the axle would've made for very good handling.

If you're looking for batteries, I would suggest ebikes.ca personally, and most of the other members here know some pretty good sources.