You can get it after the Dawn Shard is in your grubby little hands. You then can go for the Spear in four not-so-simple steps:

(SPOILER)1) Go to Nalbina and speak to July. Then go to the Imperials guarding the exit to Mophoran Highwaste. With the information you learn, go speak to Gurdy and rent a chocobo and approach the guards again. The path to Mophoran Highwaste will be open.

2) Proceed through Mophoran to the Salikawood.

3) Defeat King Bomb. He's pretty difficult at lower levels since he can replenish his HP several times.

4) Go past the boss area and follow the SW branch to the Necrohol of Nabudis. At low levels, just run to get the Spear and run back.