If I am not mistaken you would not only need the Plazmic theme
building app but you would also need the .thm files for the theme.
I don't know how many theme designers are going to be willing
to give that to someone else.
You would need access to the THM file that the theme was compiled from and very VERY few theme designers are going to give you the THM file from their theme. Alternatively U can download Plazmic content developers kit for free (Plazmic) and create your own themes!