I have a local shop that sells all kind of falim gum. The best by far (hardest) are the smaller ones. The problem is the come in small package: https://www.amazon.com/Turkish-Chewy-Y%C4%B1ld%C4%B1z-Sugar-Stick/dp/B07PN7FB2Y/ref=mp_s_a_1_1?keywords=Yildiz+gum&qid=1560687382&s=gateway&sr=8-1

These ones are just as effective and come in bigger packages: https://www.amazon.com/Falim-100-Chewing-Gum-Damla-Sakizli/dp/B005GR1WO0

Edit: Sorry thought you meant falim gum. I'm not gonna delete the respons incase you or anyone else wonders