If you could get access to Central Admin, you could increase the List View Threshold (LVT):
- Login to Central Admin
- Go to Application Management -> Manage Web Applications
- Pick the Web application for which you want to change the LVT (If you only have 1 web app plus the central admin one, the one you want to pick is the 1 web app; changing this for the central admin does you no good)
- In the ribbon above, click General Settings. That will bring down a menu, from which you should pick Resource Throttling
- Change the LVT (first item in this list) to another value and press OK, but please try to keep it to a reasonable number!
NOTE: Don't forget to change it back to a reasonable number after you done your export.
Another option is to export items in batches, using views or script.
If you can't use Central Admin or script, views is the only option I guess. Create view with filter
ID is less or equal 30.000 and another with filter
ID is greater than 30.000 for example. Export them separately then merge them in Excel.