Columbus Circle is a retro game retailer based in Japan that sells in niche video game stores as well as larger department stores (Bic Camera, Yodobashi Camera). From what I can tell, they sell online as well. You can get their stuff via Yahoo Japan, and also through eBay. Hell, ive found this on Gumtree too.
BIC Camera Columbus Circle Stand
I picked up this flyer in a BIC Camera store in Shinjuku. BIC Camera stores are plentiful in Tokyo, and they are normally adjoined to a large department store. There was a corresponding stand displaying a portable famicon clone, and some type of all-in-one console. I noticed a cool music famicom cart as well, though im not sure if that was for sale.
Advantage of some of these all in one units is that you do not need to buy an expensive upscaler device, which can host a few hundred dollars. Though part of me feels like nothing beats using original console gear.
Scan of the free flyer
Website link here: www.columbuscircle.co.jp