How do I get an older version of Adobe Audition for the trial period?

Which 'earlier version' are you referring to? The current version - certainly the beta version of it - works fine, If it isn't working for you on your machine, then that's where the problem will lie. How much experience of running Audition do you have? We appear to be short of rather a lot of information here...

There are no earlier trial versions to be had. Adobe's policy on what's available is the currrent version and its -1 -that's all.