Let me ask responders to please read my original question, especially:

A client uses item codes that are different from UPC codes, but which cross-reference on a one-to-one basis. The codes are already printed as bar codes on the items they purchase and sell.

Also:

They would like to be able to scan the bar code and have Adagio pull up the correct item, whether it be in Inventory, Order Entry, or Purchase Orders.

Thanks

Steve