I have a bash script which you could add to cron table if you run linux and have shell access. I'll just paste it here, it's short enough.
#!/bin/sh
ls -1 $1/maps/ | grep PMS$ | sed s/\.PMS// | shuf > $1/mapslist.txt
if you save it under randomize.sh then you can run it using:
$ sh randomize.sh /path/to/your/server/