Currently, Honedge drops 1-2 iron ingots 100% of the time, 1 ghast tear 50% of the time, and 1 aluminum ingot 10% of the time. Doublade drops 1-3 iron ingots 100% of the time, 1-2 ghast tears 50% of the time, 1-2 aluminum ingots 30% of the time, and 1-2 silver ingots 10% of the time. Aegislash drops 2-4 iron ingots 100% of the time, 1-3 ghast tears 50% of the time, 1-3 platinum ingots 30% of the time, and 1 Spell Tag 10% of the time. Despite each including metal swords in their design, none of them can drop any swords.
While I feel Iron Swords, Aluminum Swords, Silver Swords, or Platinum swords would make the most sense due to them resembling the swords that makes up Honedge and Doublade, you could even use a Dusk Stone Sword as a drop due to Doublade evolving into Aegislash by Dusk Stone or you could do the Rusted Sword. Or perhaps if Aegislash gets the sword drop then the drop should be a Golden Sword since that is what Aegislash's sword resembles colorwise. Either way, I feel someone in this evolution line needs to drop some kind of sword.