How to upgrade Arduino UnoR3 clock
It's really easy to take an ATmega328 chip and wire it up on it's own.  There are even instructions on the Arduino site on how to do it.  Take a look at http://www.arduino.cc/en/Main/Standalone .

You could even pull the 328 out of the Uno, add the crystal and a few caps and then program it with the Uno board.  I've done this a few times myself and it worked just fine for my needs.