After the San Bruno Fire, Home owners & buyers have a lot of concern if they live near underground pipelines that could put themsevleves and their families at risk.
So for your ease, here is a link to the Federal National Pipeline Mapping System:
This shows all the major gas pipelines, above and below ground and includes storage tanks. At the current time, this is the only resource I can find. If you know something better or that can be used in addition to this, please let me know.