Hi, can somebody help me in my looking for some good bookshop in İstanbul where I could find something about Said Nursi and Fethullah Gülen in English. I have already been to Robinson Crusoe and some shops at İstiklal Caddesi and the one in Sultanahmet...

I advise you "sahaflar" in beyazıt distict.

Check these links:

http://www.turkeytravelplanner.com/WhereToGo/Istanbul/Shopping/bookshops/index.html

http://www.timeout.com.tr/yazi_goster.php?artID=669

Did you explicitely ask for the books at Robinson Crusoe's? Can't they order them? That store is well-known for T-E translated books..