I'm from Istanbul, Turkey, and I've travelled quite a lot with all my film (in my carry-on luggage) going through x-rays. I never had a fogging problem. You probably won't transport 500 rolls in your carry- on luggage, so I would consider the special film bags containing lead. If you are still concerned, it definitely is worth contacting the customs office.(posted 8659 days ago)If you are going to stay in Istanbul for a while, I could provide you with some addresses that sell B&W photographic material. Finding any sort of Ilford or Kodak B&W film is no problem.
Getting your B&W film processed commercially can be quite difficult (not so with slide film). It depends on where you are of course. In Istanbul you can get it processed but it will be very expensive.
If you have further questions please don't hesitate to contact me.
I wish you a pleasant stay in Turkey.
Best wishes, Omar Ozenir