I have made an invitation poster
(http://www.krokodyl.org/ECposter-mail.pdf) and now I'm looking for
email addresses or web pages to send it to. We are looking for
Christian leaders (both individuals or teams) from English speaking
countries to join our Summer camp with English lessons. I'm sure there
must be some webpage to post offers and invitations like these, is it
not? Can you help me?
(see the poster for further details, I don't think it'd be fair to
paste the text here, that would be advertising)

I would try...
http://www.churchstaffing.com/