Go through all the vehicle paperwork on the off chance. After I changed the battery on my wife's 1998 Fiesta her radio went looking for the code, amongst all the bits of paper and service receipts in the book was the business card for the salesman who sold it when it was new. On the back in blue biro was a four digit number and that happened to be the code.
this is a very helpful tutorial to get your stereo code for free, and you can put a comment in this Youtube video and they will calculate code for you if you want ;)