We don't have a feature for an additional tab at this time. However we have some options for you to display the PTA/PTO information.
1. Rename the sponsor tab to "PTA Info" and then put a link to website where the information is stored. You could also do this with the calendar tab if you didn't want to use the calendar.
2. Add the PTA positions/contact info to the Teacher tab and rename the tab to be Staff & PTA or something like that. Prefix all of the titles with "PTA-" so they are easily searchable.
3. Put the PTA role information in the family records in the notes.