I got a nice one from Overclockers over a year or so ago. It was my first forage into professional mousemats as you said, Brick'n'Mortar places are useless.

At a quick glance, they don't have the one I have, but there seems to be quite a few choices from Razer, who specialise in producing computer-mice and gamer-mice, so I would look towards the direction of those. They will have all the specifications and sizes, etc there.