Actually stationers too. I have something similar on my work desk under my keyboard, it's black but has a clear plastic cover over the top which you can slide things under - I have all kinds of work info on mine, saves a lot of space on having postits and such up and much more convenient.
We order them in so not sure where from but major stationers should do them, posh ones probably will too, nicer ones, more leather like (quite a lawyer things etc... for older desks) but at a price and they tend to retain marks from cups if not careful so coasters needed.