Jane_Doe - 8:02 pm on Jul 13, 2013 (gmt 0)
Can you ask the last site owner with the correct publisher id to enter the appeal for your client? Maybe pay them to do so if they don't want to do it voluntarily? Or is the Adsense ban why they sold the site?
From what you wrote you are only allowed one appeal per Adsense account, and I'm assuming per site within that account, so did the last site owner already try this?