This is a perfect scenario for the MPN process. In the MPN process you create a special material master, (HERS material type) that gets linked to your internal material number. It also links a manufacturer's number to that material as well.
When the order is placed, you can enter the internal material number. The system will force you to then enter the manufacturer's material to order. (i.e you order the material through one vendor, but the vendor can source that material from multiple vendors).
When the material comes in, it will now have the manufacturer's number associated with it. You can now create inspection plans and assign them based on the manufacturer's number and material number. Not the vendor number.
There is a fair amount of material on the internet and in the SAP help files on this process.
This is all standard SAP and requires no development. Just some minor configuration and the creation of the master data.
Craig