I was told from a dealer that the Harvestor sabots (two that handle .45 cal) would work. Their info was sketchy so I emailed Harvestor. They said that they were not .458" caliber, but that some people had luck using them that way. They were very nice and sent me a small trial pack to see. They didn't work.
My twist is 1:48".
I've seen one brand that made .458" sabots, but couldn't figure who it was, and a Google search wasn't providing much. I believe it may have been the mmp sabots.
Thanks!