I think there is a difference between horny and promiscuous. I've dated girls from Eastern Europe, Two Czechs, One Pole, One Russian. The Polish gird was definatley the horniest but yet Poland is more conservative than other countries . As a matter of fact all her friends were horny girls too, seems they wanted to talk about sex alot. (They were from a place near Bialystok, near Lithuania and Russia, does that make a difference?)
The Russian girl was liked sex alot but not nearly as much as the Pole. One Czech girl was the about the same as the Russian and the other was a cold fish.
Maybe what it amounts to is a group of girls in a particular place that are very confortable with their sexuality and really like fucking. They are more promiscuous because they are not going to be looked down upon by their friends if they hook up with the foreigner. Possibly you could be in St. Pete, Budapest, Prague, Warsaw, ect and just have to run into the right group of girls or girl.
Sorry, I'm sure that doesn't help at all, but I think in most places you visit, you have to pick your targets well.