Current IPv4 Options

I work for a VAR and we are starting to have customers come to us to help with internet redundancy projects and they are unable to get address space from ARIN. What are the viable options here? I have read about secondary markets, transfers, auction sites, leasing, etc. Can NANOG point me in the right direction as to the most effective way to get v4 space right now in the US? And before we get into the whole IPv6 discussion, yes, yes, we are discussing this with customers as well. That being said, they still need the IPv4 space in the near-term. Thanks all, Clay Curtis