Filter choice option based on existing entries

I’m creating an app to track inventory at different locations. We have a master list of inventory items that users won’t be able to edit. However, each location has a different set of inventory items, so I want the ability for them to add the items that don’t yet exist at their location. To keep track of inventory levels across all locations, I’m putting all the inventory entries into the same Google sheet.

I’ve created a form for them to add add items from the master list. However, I want to filter out items that have already been added at this location.

I’ve found a few previous threads that might have a possible solution, but the proposed solutions seems pretty complicated. Is there an easy solution to make sure we don’t get duplicate entries for inventory items at each location?