Need references for defining Supplier-Item Number relationship in Item Master

Summary:

Need references for defining Supplier-Item Number relationship in Item Master and use this relationship in transactions.

Content (required):

We are trying to establish Item relationship with Suppliers and tried to create supplier items. But only Inactive suppliers are visible in the Supplier LOV. Active suppliers are not available for selection. Couldn't find any refences explaining this functionality. Any suggestions please?

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