How can I filter values from a ref table in the user form?

[JulioHM]

I have two tables:

• Product
• Category

The Product table has a ref column to Category, and each Product is allowed to be associated to one specific category.

Category has a Yes/No column called "available". I would like to disable some categories so that the user is no longer able to select them in the Product form view. I can't simply delete values from the Category table, since they are already in use by Product records that were registered in the past. That history needs to be available, but future products can no longer be assigned a category that is no longer marked as available.

How can I filter the Product form view to show only Category records that match a specific filter, let's say "[Category].[Available] = True" ?

That would be really helpful. 

Thanks a lot.