Teavana lists the ingredients in all their blends on their website, but this isn't enough information to replicate the blend, because there are typically many ingredients, and the proportions are still a wildcard, even if you know the order of which ingredients are in greater proportion than others.
In my opinion, Teavana's biggest strength is their blending, so you will likely find it hard to replicate any of their blends exactly, and you may find it harder to make a blend you like as much or more.
You may have better luck just trying to make your own novel blend, using theirs as inspiration or a starting point. What is it that you like about MateVana? Think about what qualities you want and then start figuring out how to make a blend that will embody the qualities that you like. You may come up with something you like even more, using this method.
I will say one thing...good Yerba mate is dirt cheap...way cheaper than even low-quality tea. So that's not going to be the limiting factor in your adventures. Shop around and find some mate that you like for a base and then go from there. Good luck!