I'm afraid to tell you that it's not possible to further process data like the percentage of availability, within the report.
You could however try to use a different template for the report. There are templates that offer optional data tables and also data files besides the graphs.
For every report template you can see if there are "Data Files available" in the title of the report. For these particular reports you are able to configure also a data export as CSV or XML. These files will then be stored in PRTG's datafolder in the subfolder "\Report PDFs".
I hope this helps.
Tech Support, Paessler AG