SKU's are probably not what you are looking for, as there is no reference that everyone uses AFAIK. Each retailer can make up there own or use the vendors.
UPC is a standard that covers (in the US upc codes) and they are unique. EAN is the equivalent in Europe and I think Japan has another. These only cover original makers.
I have an SKU # assigned to my record label and all my CD's start with the same (six I think, but I am not home) numbers. These identify me as the vendor (and theoretically some other traits i.e. entertainment/CD's).
These don't hold true for Books as they use ISBN and its derivatives. I think you are failing in your search because this DB doesn't exist. I hope I am wrong as I would love to get at that data also.
