The link for Apex codes above is for the remotes that came with their products.
There isn't a 3 or 4 digit number that represents the specific make and model of DVD you have for all remotes.
Each remote will have a list of the preprogrammed database of IR codes that you can assign with a number to a device type on that model remote. There is usually a list of these in the instructions for the remote.
If the correct codes are not already in your remote you can't add them. You can get a Logitech Harmony remote that programs from their huge online database of IR codes.