This is a very 'broad' question: Do you know someone who lives here in Istanbul already? That is your best bet.
If not, then here are a few questions for you, to help you narrow your search:
- where in Istanbul are you having your reception and ceremony?
- how many people are in the wedding party?
- what 'type' of photography are you looking for... portraits/photo-journalistic/intimate
We used a wedding planner - a family company called A'dan Z'ye (A to Z) - they are amazing and immediately they were like family! We don't speak Turkish, but they accommodated and made sure that there was someone from the family to speak English and translate for us - and everything was perfect.
I know it is pretty vague, but I hope this helps a bit, or gets you started in the right direction.
Click on each tool to see a sample.