Currently, if there is more than 30 Sprints in GreenHopper Agile Board, user is not able to select other Sprint in the Sprint list in GreenHopper's Sprint Report. There is no scroll bar on the list itself.

Refer to the screenshot below for more detail illustrations:

Workaround

Use the issue navigator and do a query like "sprint in (xxxxx)" where xxxxx is the sprint name, and let it auto-complete, after which jira will show the sprint number (e.g 159). then you can update the URL in the sprint report with that number.