If you can get a recommendation for a local, hobbyist-friendly steel shop, that will help you now and in the future. A lot of steel stores operate for industry - big orders faxed in with purchase numbers. A little guy walks in and need 6' of 2x2 box...that's great, come back Friday.
A hobbyist-oriented steel store will also do industrial supply, but you can walk in, browse their selection, request the size and length of material you need and they'll cut it for you then and there. Sometimes there's a cutting fee, sometimes there isn't, but IME when there is it is something like 2.5-5% of the total. Planning ahead can get them to cut stuff for you at lengths that work for you, but they're still much happier cutting the least possible.
You can wander into your local steel stores and get a quick idea what they're geared toward, but a recommendation will make it quicker.
Because when you spend a silly amount of money on a silly, trivial thing that will help you not one jot, you are demonstrating that you have a soul and a heart and that you are the sort of person who has no time for Which? magazine. – Jeremy Clarkson