Wald makes a steel one, Wald Cat#s 940, 945, 950, 955. These fit a standard seat clamp unlike the OEM seat posts. See p. 19 of their catalog... http://www.waldsports.com/files/WaldSports/Catalog.pdf . These are available from retailers like Niagara Cycle Works and Bikepartsusa but the images shown are wrong; look at the Wald catalog for the correct image. I don't know where to get an aluminum one.

Good luck!