I am sorry I can not give you an specific name and address in Beijing, but I will tell you how I managed to locate a seller for mine.

I asked a friend who has a restaurant to tell me about a store that will sell equipment to restaurants, and he gave me the address of one in Nanning.  I went to them, and was surprised at the many "goodies" they had, I bought a two basket deep fryer (great for chips and fish) for 200 yuan, and a darn good electrical oven like the ones back home too.  Asking price was 4600, got it for 3500.  Also bought a hand mixer, a pressure cooker, a serrated knife to cut bread, etc.

Then I had a local carpenter built me a cabinet to install the oven and microwave, with a storage shelf below and another above them.

So, if can not find a place that sells ovens, look for a store that sells restaurant equipment, and see if they carry it.

Actually, I have seen western ovens [gas] in some of the bigger department stores.

One Chinese brand also makes them [for export] and only very few Chinese people buy them as they do not roast nor bake. The brand  name is Haier.