In the Unseen Queen, Luke and Han are forced to give up their weapons:
Han's knuckles whitened around his blaster grip. "When Hutts ride swoops!"
"We would rather have it now," Raynar said. Han's blaster twisted free of his grasp and floated over, then Raynar turned to Luke. Master Skywalker?"
Luke hated to yield his weapon-especially with Alema Rar running around loose-but he would have an easier time recovering it later than fighting to keep it now. He removed the focusing crystal from the handle-the Jedi equivalent of unloading a weapon before surrendering it-and handed both the crystal and lightsaber over.
They end up leaving by jumping out of their prison cell into a waiting ship, which doesn't leave much time for recovering weapons. We even hear in the next book that Han did not get his back:
Han drew his blaster pistol- a 434 "DeathHammer," which Lando had given him to replace the trusty DL-44 that Raynar Thule had taken from on Woteba
But shortly after they leave, they find themselves the climactic battle, and Luke has a lightsaber again:
"I thought all we had to do was blow the nest ship's hyperdrive, and Mara can do that a lot easier with a shadow bomb than we can with a lightsaber and two crummy blaster pistols."
Is it ever explained how he got this lightsaber?