How and where to enter vendor item number cross reference

Dear,

For customers, we can enter a "Customer Item Cross Reference", entering both customer name/number and their part number - linked up to our internal item number.

Where and how (if possible) can I do the same for a vendor/supplier? Preferable so that I can select our item number and the vendor/supplier part number is automatically showing up, based on the vendor selected in the PO.

Thanks,

Lars