try making friends with your local metal supermarket lads.
ones at my local are great, i go in tell them what i want and they let look at their offcuts.
needed some 38mm rd other day they only had 42mm in offcuts bit but they only ever charge me scrap wt + 10%.
worst i had was needed some 2" and they only had 60mm but bit extra time turning down was worth saving i made in money.
also try local scrap metal dealers my local one saves anything that might be useful again scrap value + a bit.
got some nice 1/2" ali discs from him i used to make a set bearing installers with.
another good source is local metal collector guy, he often stops by with bits for me, as empties out couple of factory units.