Rudey,

If you are making a concerted effort to found a new alumni group, there should be an alumni development director and budget to offset the costs of that that mailing. Don't discount posting on the national fraternity website and starting and email chain to all the alum you know and encouraging them to forward the email to those in their inner circle. Hold a meeting, and encourage people to bring friends, and pay dues. Set another meeting. And another. the word will get out.

Good luck

Start with something small. Like I suggested, a meet up during happy hour is cost effective (it's free) and will result in having alumni come together and feeling comfortable with each other. From there, increase steadily until you can have a fully functioning Alum Association.