I have looked extensively and there does not seem to be a way to provide a report based on used/un-used ports over any period of time that used to exist in Inventory Manager.
There was youtube video posted about archives but it doesn't outline how to generate the reports.
Reporting functionality in the Extreme Management Center requires a license other than NMS-Base. If you don't see reports that indicates that you have an NMS-Base license and should contact sales to purchase an upgrade.
It's not a report, but if you telnet/ssh into the switch, you can run the following command to get this info ...
show port info detail | include Port:|Link\sState:|Link\sUps:|Link\sDowns
It's been working pretty well for me. Credit due to whoever posted that on another thread. I just pasted it away in a text file and use it all the time.