You just need to look in the right places br0. IMO, look for well educated girls. The more well educated she is, the less religious she is likely to be.
+1.
Keep your eyes peeled. Don't expect a girl to be outwardly like you - girls tend to be more personal with their religious views. Plus, you don't want a girl who thinks exactly like you, that would be boring. What you really want in practical terms sounds like a girl brought up in a liberal Muslim background who is not particularly religious.
From the sounds of it you've gone out with a few Muslim girls and were honest from the start - that's great, what I will say is don't let the ex-Muslim thing define you. Were you maybe talking about religion alot with them or trying to dissuade them away from Islam? If you are looking for a girl who you can take home to your (I'm assuming religious) parents then it's probably more important she is from a Muslim background, but try and gauge early on how much she is invested in Islam, because she will likely not take kindly to you trying to pull her away from Allah.