Steel Furniture Manufacturing?

Hi everyone! I came across this forum looking for business ideas and I have an immense interest in designing furniture and upscale lighting applications. This seems like a friendly place to ask for advice. I`m not sure at this stage whether my hobby will develop into a business, but let`s say if I wanted to take it to the next step, where do I go? Specifically, how do I get a hold of a company that manufactures stainless steel or aluminum extrusions (e.g. the body of a lamp, or a steel rack)? I`m not even sure what the technically correct term for this type of manufacturing is, which makes it hard to look for information online. Also, does anybody know what kind of volume these places usually deal in? I`m not sure I`m willing to invest a lot into an untested idea. All this is assuming I already have a prototype design in CAD, or something similar (I don`t, but I like to plan 2 steps ahead). Does anyone have experience in this field?
Thanks for reading.