Hidelisa Centro in Puerto Plata has a large range of rods, hooks, hangers and material. You should be able to find someone to make the curtains for you.
Maybe not in Sosua, but I had all my curtains made in Sabaneta Patricia Decoraciones.
You can say, a small Hidalisa, you really do not have to go to POP, in her store she also has everything.
And important, a incredible great service.