For the sake of the question, I'll look through Sandstorm. It kinda defeats the purpose to take Touchstone just to get the Endurance feat, though.
Also, I just learned that even though we're in an environment that's hot as hell, the DM's not allowing Sandstorm for "balance issues."
EDIT: Salt Sanctuary in Sandstorm gives Improved Heat Endurance, and allows for Parching Touch as an SLA, which is honestly pretty impressive.