As seen here Mraize has an Aviar. The problem is that First of the Sun, the planet that Aviar come from, does not have a Perpendicularity, as stated in Arcanum Unbounded. This being the case, how did Mraize get to First of the Sun to get an Aviar?
I remember reading an interview with Brandon Sanderson where somebody asked a simliar question regarding Mraize's Aviar. (I can't seem to find the source). Brandon States: "If it's called an Aviar, it's origin is First of the Sun."
Edit: In Arcanum Unbounded, I found this regarding First of the Sun:
I have not been able to discover why, or how this perpendicularity exists. There is certainly no Shard residing in the system. I cannot say what is happening, only that this feature must hint at things that occurred in the past of the planet. There is likely Investiture here somewhere as well, though I have not yet had a chance to investigate First of the Sun myself. The area around the perpendicularity is extremely dangerous, and the few expeditions sent there from Silverlight have not returned.
So there is definitely a Perpendicularity on First of the Sun, but we don't know why. I guess Mraize was able to risk it and grab an Aviar around the perpendicularity.