Thanks for the great suggestion, Nick. Please don’t forget to vote for it, as every vote counts 
For more on how we handle feature requests, please see 💡 Posting ideas & feature requests for Breww 💙.
I see you’ve voted for Remove specific sites from price lists (or only show some site(s) stock) already, but for anyone else looking at this, that other feature request is relevant there.
Additionally, the Breww Trade Store might be worth a look as your customers can get live pricing and availability (as well as place orders). It also understands which sites customers can have orders fulfilled from, and so shows the correct stock availability.