I might suggest that you consider replacing both bars at the same time. When I was faced with a similar situation, technicians at three different hitch shops told me the same thing. It will likely be VERY difficult to get two bars with differing amounts of use properly adjusted (through time, the bars tend to take a set based on the trailer/tow vehicle combination that evidently can interfere with being able to properly adjust the setup when bars from two different setups are mixed), and it can be quite difficult to get two bars with the same weight rating - - especially if the manufacturer didn't clearly mark the weight rating of the bars.
Reese still manufactures the heavy duty "round bar" hitch, so the replacement weight distributing bars should still be available. The hitch is still listed on their site at:
Reese Trailer Hitches
Good luck with finding a solution to your hitch problem.