Several bus tours are readily available in Greece...see link below for some good examples.
http://www.athenstours.net/?event=offer.type&productType=BUS&mpt=3911&name=Bus%20Tours%20in%20Athens
http://www.athenstours.net/?event=offer.type&productType=BUS&mpt=3911&name=Bus%20Tours%20in%20Athens