You are taking Nulled in other direction.
Let me explain a Nulled theme is the theme where you remove or change the source codes of the theme which will not ask for purchase code or activation code.
So, what I did is I have a theme from themeforest named ????theme.
When you install it it will ask you for purchase code.
What I do is remove the specific code which would not ask for purchase code.
This way it is Nulled.
If any way I give you premium theme you can never use it without purchase code.
There are some themes like Genesis which do not ask for purchase code.
But, there are few people who also inject malicious code.