Your best be would be through local governmental agencies (park, highway,etc.)or churches or corporate entities having land set aside for other future uses. They may offer the use for a limited time however. Public land is always best because of the tradition of The Commons. Municipalities often have odd pieces of land that could be dedicated to Community Gardens, especially if a CG won't cost them much.

Marshall

Here in Portage, WI we brainstormed "public" places around the city that we thought might be good spots, then went to them with our idea. For a variety of reasons, none of these spots worked out, and out of desparation, we finally put an article in the paper (as a news release, not an ad) about what our group was trying to do and what we needed in terms of land. We actually had several calls from that article and went with the one that best suited our plan. It turned out to be a place we never would have dreamed of...someone's front yard!! Albeit, a very long front yard--and their teenage son appreciated no longer having to mow so much lawn! Good luck to you.