SSH usually gives you full access to a shell, thus all the commands you can use from the command line should be avialable. Therefore, you can use something like ls to look at all filenames in a directory and choose the most recent name from them, or search the output of ls, etc. (with the appropriate options) to find the file with the latest timestamp. Or you might be able to run perl on the machine through SSH to do this task for you and return the filename over SSH to your script.

You may want to look at the modules Net::SSH, Net::SCP, Net::SSH::Perl, IPC::Open2, and/or IPC::Open3. (The latter two help you open a multidirectional pipe to a program, the first two are interfaces to the ssh and scp command line programs, and Net::SSH::Perl is SSH implemented in perl.)