Boxtaboy's route is absolutely the best one ... but if for some reason that doesn't work, you might want to try this site and pay the money ... http://www.radio-code.com/
I thought it look liked a rip-off site as it is quite cheaply done but when my wife lost the code in her Mercedes SUV I decided to give it a try. Presto -- 15 minutes after sending my money I got the code. Not saying they are 100% bullet proof but it worked for me.