I would like to find names as well as addresses and e-mail addresses
of Chiefs of Governments in the world.

Dear vico1936,

It proved impossible to find a directory that includes both an
up-to-date list of current heads of government and their contact
information. However, I have found two seperate sources you can
combine:

I.
The CIA Directory of Chiefs of State and Cabinet Members of Foreign
Governments, current as of 17 June 2005
http://www.cia.gov/cia/publications/chiefs/

II.
The List of Addresses of the Politicians of the World
http://www.fortunecity.com/greenfield/swallowtail/408/addresses.htm

Please note that the names in the latter list are not up-to-date
anymore! Therefore, it will be necessary to compare the entries with
the names of the current world leaders in the CIA database. However,
it is unlikely that the mailing addresses of many offices have changed
in the meantime, if any at all.

This is the best I could find. I hope that it will meet your needs.
Best regards,
Scriptor