Hi, lidar datasets exist only at specific areas, such as main cities (Athens, Thessaloniki). For other areas, only where big projects (like Transadriatic Pipeline) take place. Another accurate and reliable similar dataset that can be usefull, is the DSM production from orthophoto matching by the National Cadastre & Mapping Agency S.A. (http://www.ktimatologio.gr), from the period 2007-2009. This project took place for the needs of orthophoto covering of all Greece. By a simple request, i think you can have it for free.
As far as i know now is running a new contract for the update of the old orthophotos.