Does anyone make steel handlebars?
apart from cheap bikes i can't imagine anyone making steel handle bars due to the weight of them.
As for damping vibration, on a mountain bike thats not really the job of the bars, its the job of the fork and the tyres, if you need the bars to absorb shock then the rest of your setup needs a lot of work
for the record, carbonfibre has some of the best shock absorbing properties of common bike materials and there are plenty of carbon bars out there