I was wondering, do you want small as in small footprint, slim, or just small total volume?
There's always the compact mechanical keyboards like the Pure, Poker or HHKB (Or even my HE0100 that is both compact with scissor switch level slim keys, there's a MD01B0 [White version] on Yahoo Auctions right now), the compact layout may not be traditional but I think the size fits a tablet more. And you get mechanical switches there as well.