Talk to a distributor of metal products and find out who customers are.... you can probably work out getting some scrap from them or from scrap yard they sell to.
-- Way too expensive to buy as commodity item unless you have a paying project.
-- Scrap route is the way to go for larger pieces; just get your hands on the right type of equipment to properly cut, drill, bend and weld it.
Pipe flange, and tubing companies; heat exchangers; scientific and industrial business suppliers are a good source. Down here in Texas, the chemical and refining industries that are the major customers.
