The problem with listing factories is the sheer numbers. This site has 109,268 Fabrication Companies in the US.
http://www.manta.com/mb_33_E5_000/fabrication
It has employees per site which might be a useful to make that number more manageable, but they are not listed in a way which is easily accessible.
Edit. Oh neat they did add filters.
http://www.manta.com/mb_33_E5_000/fa...ompany_emp=E05
Here are 101 Fabrication Plants with over 750 employees.