Steve, here is my only recommendation.
http://www.ironmind-store.com/S-Cubed-Bar153/productinfo/1223/
IronMind's S-Cubed Bar is insanely strong and stiff. It's a hefty price tag $650 (without shipping), but you should never have to buy another bar again in a normal lifetime of lifting.
Coincidentally (since you are interested in it for the Inman Mile), the only time I've had a chance to use an S-Cubed Bar was with at an acquaintance's house a few years ago. He was moving overseas and selling all of his lifting equipment. He told me he had used his S-Cubed Bar for Inman Mile training. He said he didn't mind dropping it off his shoulders when he became exhausted, because it was so tough that it didn't hurt the bar in any way when he dropped it. On dirt usually, but on concrete once (!) from what he told me. His bodyweight was about 220lbs, so his minimum training weight was 330lbs. But he mentioned he preferred training with double bodyweight and heavier, because it made 330lbs feel "light." He said that even at 500lbs, the S-Cubed Bar didn't bend or flex at all when he walked.