Neither the commission, nor the parliament (or Eurostat) are providing this information in a comprehensive way.
For the elections of 2004 onwards post-election reports exist (http://www.europarl.europa.eu/pdf/eurobarometre/2014/post/post_ee2014_sociodemographic_annex_en.pdf).
So I would rather need information for the elections before 2004. Thank your for your support!
Torben