There appears to be a limit on the shift calendar for the campaign field

When viewing the Shift Calendar there is a limit of 1000 campaigns in the dropdown list, we have over 2500 campaigns. Does anyone have any ideas on how we either may be able to increase this or split the calendar view into criteria. i.e. All our Volunteer Supervisor staff exist in Districts so if we could limit the campaign drop down to a district this would reduce the number of campaigns that would need to appear in the list.