Here is a port of the Rotten Tomatoes Scraper for Plex. Let me know the bugs you find. This is the first release and it may not scrape every movie correctly. Use at your own risk.
Special thanks to Red Tape Media for the xmbc code.
To add it to plex
Navigate to the plex app in your applications folder
right click on the app and click “show package contents”
Contents > Resources > Plex > System > Scrapers > video
Paste both the .xml file and the png in the video folder