I swear the different Craigslists have different rules about postings and how long they can stay up. On my local one everything older than a week is gone and you have to remember which ads were posted before. The nearby ones hold onto postings much longer. Or is that true of every CL that the "local" one cuts off ads that are older than a week?
There are selling groups through the major email/group services like Yahoo for sales with shipping and selling groups on Facebook for local sales.