think i might give them a ringI get most of my material for projects and the like from Pheonix steel in Hebburn.
But for practice try calling into some location fabrication company's you might find a nice one that will sell you bits of scrap, sometimes for a few quid to go in the tea pot.
they give u it freeTry your local scrap yard. The cuttings from most of the fabrication shops end up there and if you get friendly with some of the staff they will usually let you take stuff away for the scrap value, sometimes free! Then when you've finished practicing with it you can bring it back for scrap and get your money back!
i doubt that verry much they wouldnt give u the steam of there sh ,,it if they had a use for it 
Not worth faffing about with scrap, you might have to spend too much time and effort / cost preping it. Just order black mild strip, 3 x 20, 5 x 25 ect, and cut it into 150mm lengths.
When every peice is welded to every other piece you can weigh it in, and start again.
