You could try pushing buttons 1 and 6 or 2 and 5 together. You might manage to get the serial number to come up on the display. It will be a number starting with a "V" or an "M" and this will be followed by a six digit number. So, the serial number will look like this:

M123456 or V123456

The display will scroll through a lot of other numbers but they aren't the radio serial number.

From what you've already said about your radio I rather think that your serial number is going to be a "V" one, in which case, there's nobody on this forum who can give you the code, I'm afraid. Your only options for a "V" code are a Ford Main Dealer or there are sellers on Ebay who say they can do them.

If it's an "M" number then you can obtain the code from these people:

www.pumapeople.com/decode.php