Have you tried contacting CHADD about setting one up for your area? I know that often they just need someone willing to spearhead the idea and they can provide you with the support, guidance and materials for getting it done.
If you decide you want to do it, you could start by looking for a location in which to hold your meetings. Often churches, community centers, libraries or even schools are willing to let a group like that come in once a month.
You could utilize your school district to distribute the information to the schools. Some districts have a community advisory committee (CAC) that acts as liaison between the parents and outside support service groups. In our community, the CAC is made up of parents and administrators. They meet monthly to present programs on everything from how to set up a 504 plan or IEP, to having outside support groups (like CHADD, autism groups, etc.) come in to present.
I think your best bet is to contact CHADD national and ask for their help.