I went in to a lovely undies shop in Fetiyhe in May, they had a basket of bits on the counter which I am pretty sure had some rolled up straps in not sure about invisible ones but could have been, I remember as I bought a few of those bra extenders out of the same basket. They were really friendly and had some lovely stuff all reasonably priced, only problem is I can not think of the name, it was on the same side of the street as the popular chemist opposite Migros and the change shop, hope this is a help