C.K.
you might want to try joining a mom's club. those typically find playgroups based on the age of your child although one of our groups recently stopped meeting regularly with preschool schedules. the oldest of our kids is 4.5 years. http://www.momsclubspringfieldva.org/
there are the local rec centers that offer classes by age.
http://www.fairfaxcounty.gov/parks/parktakes.htm
i met a really good friend who just approached me at a park with my son one afternoon. they were looking at houses in the neighborhood. she was not even with her son at the time.
best of luck.