Looking for rv bathroom parts. Anyone have good sources?

I have a horse trailer with a small living quarters that I would like to build out. We already have a generator, ac, and heater, and we know where to get everything but the bathroom materials. We would like to put in one of those bathroom units that combines the toilet and shower. I've seen them at trailer sales lots. Unfortunately, I can't find anywhere that will sell the units. The ones I've seen have a very sharp corner angle that utilizes all the space in the trailer, with the toilet actually inside the shower stall. I believe there is a holding tank underneath the pan. Does anyone know where I can find one of these and approximately what they cost? Thanks