Thevenin Equivalent Circuit of Ideal Independent Current Source
Your calculation is right. the only thing you need to consider is the definition of an ideal DC current source and that is a source that regardless of the voltage between its terminals, its current is constant. with this definition you can't replace them with each other.
Nevertheless, Thevenin and Norton equivalents are methods for simplify complicated circuits and not for replacing a single source with another.
It worth mentioning that in the real world there are no ideal sources, so this would never happen.