List Duplicates (Don't Remove)

Hi guys,
I am looking for a way to find and separate the duplicates in the inventory. It turned out the some of books in my stores inventory have been listed more than once on ebay. That is causing pricing issues and mismanagement of inventory.
Now, i have a file which contains ItemIDs (Unique) in one column and ISBN (may not be unique) in 2nd column. The only way to remove the duplicated books is to provide their ItemID. How can i find and separately list duplicated ISBN (Remember ItemID is unique for even duplicated ISBN). There must be one ISBN value left in the list because i just want to remove duplicated value, not the original one.
Please review the attached file. Thank you very much