You can purchase at Dalaman on arrival but the last time I used it, they were restricting what you could buy. However they did 'jiggle' things about because one Turkish man wanted spirits which I didn't so the girl allowed me his tobacco allowance and gave him my spirit allowance. Like everywhere else, it will depend on who's at the check out and how they feel on the day but you can buy in addition to what you bought in the UK. A couple of words in Turkish and a smile can help. Good luck.