how to link more than one item master org to RBS

Summary:

My customer has two Company , each company has two different bus and different legal entity

So in the project i will create two rbs for each company so i want access each rbs to the item master org

but i found the if i need to user the material items , should link the resource class" material items" with item master org

but the resource class linked only with one item master org but my client has two item master org

so what should i do in this case

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