Where did Ezra get the kyber crystal for his new Lightsaber in the Ahsoka series? 

Very nice theory, but I think the explanation is simpler. Ezra lived in the other galaxy for what, thirteen years? And Jedi are known there. I'd say, he found a new crystal there. There's no way, he didn't mediate enough, for another crystal to call to him in all those years.

Huyang could’ve had a collection of crystals in storage aside from parts, which could likely be more accurate. The crystals may not have been kyber, being that you don’t need a specific kind of crystal for a lightsaber as long as it’s maybe durable, Luke of course forged a synthetic green one and Mace Windu had a Hurrikaine Amethyst (according to a book I read).

If you watch the scene where Vader breaks the saberbalster, it looks an awful lot like Ezra picked up the crystal. I frame-by-framed it and I'm 90% sure that's how it happened.

Or he picked it up after Vader turned his attention towards Asohka.

Very nice theory, I follow you to hear more !

You can absolutely use a kyber crystal that didn't call to you. Look at Vader's lightsaber

I assumed it was his original he received at the Jedi Temple at Lothal.

How did you make both your Ezra suits