You can try to buy online from an EU dealer (the one of my previous link has H stem bikes in stock)
or another one. You will probably have to pay import taxes into Turkey.
What seems well the case, is that Brompton doesn't like to build custom bikes anymore and that Brompton Junction shops receive easier custom orders than other dealers.
Brompton has also now direct online shops in every European country that compete against dealers (people buying bikes online can either have the online bought bike delivered to their home or to a local dealer).