A specific one? Or any in general?
I'm more inclined to sort of go on meditations and if I happen to meet one in those altered states of mind, then great. They're more likely to be found where, umm, wherever they are more likely to be found. But my summonings always rely on my having met them before, then I just think of them and also think "Yes, YOU. GET OVER HERE." It's no guarantee that they will, but sometimes they do.