Terraria, goblin tinker

It’s an odd situation, and I can’t say for certain what should’ve happened in that situation, I think it should’ve been dropped. But, if the item wasn’t and it’s now after the fact, there’s nothing you can do in vanilla terraria.

However, if you’re playing version 1.3.5 or earlier, you have the option of using mods through T-Mod Loader. Another alternative, is using some form of save game modifier, to alter your character’s inventory or your world.

I must warn though that this is “cheating” in the sense you’re obtaining items in a way that isn’t intended, and I wouldn’t recommend going down this route.