The MASTER SKU concept originates in Inventory/Warehouse Management Systems where, for either procurement or sales reasons, a single product is referenced with more than one SKU.  It is essentially an alias for a product. 

In Odoo, you would store you Company SKU in the Internal Reference field of the Product, and the Master SKU in the Product Code field of the Vendor Pricelist associated to the Product.  

The Internal Reference field should not be the UPC of the Product.  Both a UPC and SKU are numeric-based codes assigned to products, but UPC's and are created outside your Company and can change if the Manufacturer of the product changes, if a new Manufacturer ends up making the product moving forward, or if the original Manufacturer is sold to another Manufacturer. With a Company SKU (Internal Reference) you can always maintain a unique and unchanging code to identify a product no matter who manufactures it and/or who sells it to you.

Back to Master / Alternate SKU's:

Procurement:  A product may have more than one SKU when purchased from a Vendor (your situation)

Sales: A product may have more than one SKU when sold.  An “Ebay” SKU, an “Amazon” SKU, etc. These are often known as "listing" SKU's, "seller" SKU's, or "marketplace" SKU's. 

Both can be supported with minor customization:

Procurement:

The Supplier Pricelist can be extended to support the MASTER / ALTERNATE SKU concept:

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This POC took just about 3 hours. Your Odoo Consultant or an Odoo Partner can help meet your specific needs within a similar timeframe.  A module was needed to override the name_get of the Vendor Pricelist to show the Alternate SKU, but everything else was done via Odoo Studio. 

Possible additional needs are (1) merging of existing SKU's that are already in Odoo as products; and (2) allowing users to select an alternate on a Purchase Order (instead of just seeing the alternate and transposing the new part into the DESCRIPTION field).