Rand is the brand name for a comany called Codiam & Rand which is partners with Tiffany in Debeers diamond site. They only sell finished rings with their Tiffany quality stones so even if you find a better store who has the ring in stock, it is going to come already made. I buy quite a few bigger diamonds from them but on their branded "Rand" jewelery, I will not pay the premium. Most of their product runs more to rounds and I doubt if you are going to find the ring in a cushion.
I don''t have this ring either, but have something kind of similar. It''s the Danhov Meno (can''t remember the style #) and I have it with a cushion. Other PS''ers have this ring as well (both round and cushion) and have posted pictures. Search the threads for ''Danhov'' and you should be able to find them. I think the prongs for the cushion look more like the photo you posted... they come up straight on the sides. I had tried the setting on set with a round and the sides were a little different. The Rand also looks a bit like the Daniel K Regal. You can also find photos of it here by searching the threads.