How to export a date range in Calendar
A workaround would be:


Create a temporary calendar from File>New Calendar.
Mark the calendars you want to export:


Depending on the time range you want to export select week or month view:


Go to the week or month you want to export, press ⌘A to select all events and ⌘C to copy them.
Select the temporary calendar:



and press ⌘V to paste all previously copied events. 
Export the temporary calendar as an ics file:


Delete the temporary calendar with Edit>Delete.