Tub shower conversion help

We are in the thick of a bathroom remodel, and have removed a separate shower enclosure completely with the hope of adding a shower to our existing tub. The tub currently in the bathroom is a drop in style tub, and it sits at least a foot away from the wall on each side. On the end of the tub where the existing plumbing is there is a window, which will make wall mounting a shower impossible. I am hoping to find appropriate hardware to work from the existing plumbing that rests at the top of a tiled area and install an exposed shower conversion kit, but am having trouble locating the appropriate kit for my needs. I know that such a thing must exist. It will need to stand freely from where the tub fixture was placed, with an overhead shower such as would be used for a clawfoot or freestanding tub, but the mounting is on the top rather than the inside of the tub. I don't know if any of this is makin sense, but any help to send me looking in the right direction would be greatly appreciated.