I'm not entirely sure what kindof work you're looing for, but I know of a few machine shops in my area that will sub out extra work when they are busy! While this may be much less common in your local market it's worth a shot to touch base with some of the machine shops and see if they ever sub anything out.
I would avoid LLC if possible due to double taxation, but if you're making parts that can kill someone like structural motorcycle, automotive, or aircraft parts it's not a bad idea! If you are just performing work for other people you can get by without an LLC if you check everything against specifications and make sure it's perfect before it goes out. If you can meet specifications every time the liability usually falls on the engineer or designer. What would you be producing?