Steel, you get a lot of bang for the buck and can make all kinds of things with it. Nice to have extra on hand to make things with.
So yeah, just go to your local welder/fabricator. Tell them what you want to do and they will help you out. They may just give you the scrap pieces cause they have already been paid for by the job they ran through.
Go in there with some of that RustyRatRod charm, tell them you are doing classic car engines and they will want to help you out. Give them the opportunity to say, Yes !
