WP Theme that when searching will bring up multiple results for linked SKU numbers

Hi,
I have a client who is after a solution to a problem they are having. Essentially they have a massive database of products that need to be centrally searchable. The catch is, the suppliers of the products often run out of items, and when they get them back in stock or have a similar one they often create an entirely new SKU number for the same/similar product. My question is, is there a way when the client searches the site for a specific SKU and it is say sold out that other products related to that search would come up as suggested items?
Essentially can you link SKU numbers to others?
And would anyone know of a suitable theme for this sort of thing? Preferably WP.
Thanks