Hi
If you're in Europe I would look to leicashop.com or maybe contact Jürgen Kuschnick (THE great rolleiflex repairman in europe)to see if he has any for sale to be sure to get a good one.
on leicashop.com there doesn't seem to be any 2.8f's for sale at the moment, but there's this: https://www.leicashop.com/vintage/ro...x--p-3531.html

Which seems to be a rolleiflex E2. So you can interchange the viewfinder and focussing screen as with the F.