Where is this guitar from and how do I get one for my sim?

It's the failed version of the guitar you can craft on the woodworking table. It should be in debug if you don't want to craft it.

My tip for crafting failures is to start crafting with secondary uncomfortable moodlets, but an overpowering positive one like focused, about to expire. As long as you've started the item, the sim will finish it even if uncomfortable, and il will most likely be bad.