My non-ferrous suppliers are industrial and most of what I order is full 3m or 5m lengths of bar stock or 4' x 8' sheets of sheet/plate, they will get 1/2 or 1/4 sheets of plate or sheet in to order for me but they don't do it for walk ins/non-repeat customers, it sounds like you need somewhere that does off-cuts.
If you were closer I could probably sort you out from my personal stock but the drive would probably make it uneconomical and I don't post anything I haven't worked on,
Regards,
Nick