Hi @Anil_Singh, I think the only legitimate way for this, is to get it directly from the theme developer or brand. Here are some ways you can get it:
Email the theme developer and ask for a review copy. You have to review the theme on your blog + you get to use the theme for free!
Email the theme developer and ask for a giveaway copy.
If your friends have this theme, you can request them to share it with you.
Pick 4-5 Bloggers who need this theme and you can group-buy the theme. By this, you'll be investing less and you can get this theme!
I wouldn't suggest you use any pirated ones available online, even if you are getting a $100 theme for free, you don't really want to risk your website's security by this. Best wishes!