What supply? They have all they need in their country.

A no-fly zone is tricky as well. The Iraq NFZs haven't exactly a good reputation, as they were mis-used to bully Iraq for a decade, long after the end of the short shi'ite uprising. The Iraq NFZs also artificially held an otherwise long-resolved conflict (Kuwait as liberated already) lingering for a decade.

NFZs are also an infringement on the sovereignty of Libya. The UN will likely not step over this Rubicon unless
- Libya is expelled
- Libya's Ghaddafi government outlawed as waging war against its people, not just its armed opposition (war crimes)
- another Libyan government than Ghaddafi's get international recognition (and agrees with foreign meddling in domestic affairs)


The principles of the UN are an important component of the national security for most countries, they're a huge red line in international politics.
The U.S. got away with violations thanks to its UNSC veto right, its networking with allies and its sheer size, but the potential for political power loss and backlash has always been huge.