Calling Rubber Plant Experts! Where to buy Fiscus Elastica Black Prince?

I’m trying to track down a certain variety of rubber plant - Black Prince and Black Knight have very dark leaves with bronze (as opposed to red) tones on the leaf underside.

Does anyone know where I can buy online in the UK? I’ve searched high and low!

Failing that, does anyone know of any similar varieties with the really dark leaves? I know sometimes one variety is called several things:

Burgundy, Black Knight and Abidjan are all dark, is black prince actually one of these?  

Thanks for your help!!