A little background:

I need to generate a 40KHz frequency as accurately as possible.

(One of my other posts is here: Stable frequency generation)

My code is solid- I'm using an Uno R3 and generating the most accurate frequency I can at this point. The only way to get a more accurate frequency is to upgrade the ceramic resonator to a crystal oscillator.

So, my over-arching question is: How do I actually upgrade the ceramic resonator to a crystal oscillator?

Things I'm considering are:

Is it worth it to actually upgrade my Uno R3 - and is it even possible? Is there a clone that drives the ATMega328p with a crystal oscillator that I could use instead? Is there simply just a better model for this application?