I'm currently in chapter 2 and I am supposed to find a gear wheel from the Old Mine in order to let Ian give me access to the minecrawler nest.
However I found the gear wheel when I first got into the Old Mine but I think I sold the gear wheel to a vendor or just dropped it somewhere.

I don't feel like making a new character just because the game didn't tell me that the "junk item" was an important piece for the main quest. Is there a workaround for this? Cheats or something so I can get a gear wheel or just bypass the whole thing?

First rule of junk items - there are no junk items.

BTW, if you're playing with the unofficial patch you'll probably need to use the cheat mode later on. One of the later quests will involve your character turning a certain wheel in the mountains. He tends to get stuck in an infinitely looping animation. Cheat mode on, F8, cheat mode off.

Thanks for the advice. I can now continue the game. I'm currently in Chapter IV!

I marked Kuchenschlachter's quick reply for a solution.

Thanks guys!