To be able to do item tracking on a specific item, you would have to create a unique entry for every single item in the database. As it's currently written, you have one entry for each item type and a database field on that entry for the quantity of that item, which makes tracking of a specific item impossible.
There might be a way to track items such that you add another field in the item's entry for that person pointing to which store it was purchased from. A problem arises from that should someone purchase the same item from multiple stores, as it would combine them all into the same item in the person's inventory. You would need to add code such that items bought from various stores would be kept in seperate entries; however, your users might become a little bit frustrated by having multiple entries of the same item in their inventory. Another problem arises if they trade the item or sell it in their own store. You'll have to code such that it appends the previous 'purchased from' entry rather than replacing it.
However, if you just want to receive a PM including a small message and the names of the buyer and item, then Prizem has already released an add-on that adds that functionality.