The Bluetooth keyboards are Bluetooth only.
Wired USB keyboard, that size? Never seen one. Would love to have one myself; I've wanted to homebrew a waist-pack PC with wrist keyboard and "google glass" style screen, since approximately a half hour after the dawn of time. I've even got a viewfinder CRT out of an old camcorder that I could use as the display if I hooked it up right. Trouble is I don't trust BT to not interfere with everyone else and screw me up too... that, and I'd need to make it work with a battery.
Now that I think about it... I think I've seen one such keyboard literally once ever, either by luck on eBay or on some other website. Don't remember since it was at least five years ago. The thing commanded a princely sum, too... like $150.
It occurs to me as well that you might be able to get an industrial/commercial duty wrist PC off eBay (be prepared to pay multiple hundreds of dollars) and doof around with its built-in keyboard... or do something with part of a cell phone and a Teensy... but that's real jerry-rigging at best. There are also keyboards floating around for old IPAQ PDAs that may be useful somehow... but you'd have to reverse-engineer them and they look like they'd be horrible to use to begin with, you don't even get most PC function keys (TAB, CTRL, ALT, etc).
Good luck, and let me know if you find one...