I know that there is a Tassoulis from Kiveri living in my neighborhood in Chicago. According to my dad, who is from Kiveri as well, he's in his 70's. He believes that his father's name was Athanasios. This may sound crazy, however if you're ever in Kiveri, the new cemetary is next to the soccer field. I think there is an ossuary located on the grounds Greeks tend to exhume the bodies five years after death and place the bones in the ossuary. You may have some luck there. Contact me if you have questions.