The code will not be available for free (using the serial number) from anywhere on the Internet
The Main Merc Dealer will have to look your serial sumber up on the original factory database (providing they are willing to do it!)..If your radio has been recoded in the past to a different number then you will NOT get a refund !
The best option is to take it into a Decode Service or your local Car Radio /Audio Store who will connect it to a laptop and read / recode the memory chip (EEPROM)
This only takes a few minutes and should not be too expensive
my friend, I am in Albania, and it is impossible to do so as you say here because there are no such services, so I'm looking at this way. Sorry for my English