I am not aware of any Challenger "Meeet and Greet" clubs. There are a few MOPAR clubs. In each geographic area, however, there are cruises and car shows. Check out the links in the Regional thread on this web site. See: http://www.challengerforum.com/f39/
Here in Tucson, we have the Tucson Mopar Car Club that meets the first Saturday of every other month (next meet is in August) at the Larry H. Miller dealership. One of my co-workers gave me an invite, so I might hit the meeting if I can.