I had the same trouble some months back and telephoned my local L/Rover main dealer for help.
After giving him my details and the VIN number and registration number of the vehicle he gave me the code over the phone.
Hope this helps
If you still have the OE radio, Harley's instructions will work fine. If it has ever been changed, you need to pull it out enough to get its SN off the sticker. Give that to the dealer & he can give you the code, but you may have to offer some kind of proof that you do own that radio.