I don't know how small your package needs to be, but you might want to try the microchip explorer 16 board.
it comes with two processors on the board.
One is a pic18F4550 which has USB capabilities, but the firmware needs to be updated in order for it work. This should be able to be done via microchip code generator for USB firmware.
the second processors is a 16bit pic24, which you can buy a plug in for that will give it USB capabilities. This is about as off the shelf as i could think of, both would need to be programmed for your purpose, but i believe that the microchip code generator would be able to take care of any of that.
it might be a bit expensive, i don't remember what the explorer 16 boards are running.
you work at microchip?