Expose Vendor Code found in the Purchase Order Line Item without exposing all other Vendor Codes found in the Item Record

Solution:
 
1) Navigate to List > Search > Saved Searches > New
2) Select Transactions as search type
3) Criteria tab: Type = Purchase Order
     Formula(Numeric) > Formula: DECODE({item.othervendor},{vendor.entityid},1,0) > Value = 1 > click Set
4) Results tab:  Item fields > choose Vendor Code

Note: The formula above filters only items with the same vendor as it is on the PO.