PN. Useful Site for Internships although is not so much for Research Scientists.
Europe-Internship is an organization founded in 2011 with the purpose to create a platform to bring students and companies together. As an answer to the rising demand for internships in Europe through mobility programs we created this website trying to make it easier for both companies and students.
You may check here for Internships in Greece http://www.europe-internship.com/placements/internships-in-greece/