How open are Turkish girls to dating non-Muslim/non-Turkish men?

Very open.

You are talking about the religious rules. There are many people breaking them to different extents. There is really no statistic on it, so I can't tell you for sure, but it doesn't seem to me the majority of the Turks are devoted Muslims. Also, it's partially about the traditions rather than the religion. For example, it is forbidden for Muslim men to marry non-Muslim women, other than true Christian or Jewish women, too, but it doesn't seem anybody questions the religion of a foreign woman a Turkish man gets married, the religion generally only comes to their mind, when it's a foreign man interested in a Turkish woman, but that's also generally in rural areas or amongst more traditional people. So, yes, there are many Turkish girls that dated, dates or would date a non-Muslim.

yes I've seen a Turkish girl and a n*gger kissing today and they where looking at me as if I'm sort of alien