Some solutions are: post the call on http://iuoma-network.ning.com/group/mail-art-projects , invite the community by e-mail,...
Luz, es facil!
Really, just let us know the theme, the deadline, the size limits, where to send, and we'll be there! I got 148 pieces of Mail Art for my Bicycle themed show.
Use Ti Ar Raden's link where to post your information.