Sponsorship for blogspot blog? Are you joking? I bet no company will do sponsorship unless you conduct giveaway from your own pocket. So, please move to a custom domain and self-hosted website. This may increase the possibility of sponsorship.
And yeah, you can contact the company itself saying that your domain is related to this niche, monthly visitors, etc to get sponsorship. But I believe no company will give sponsorship for a blogspot blog.
I am not trying to discourage you but yeah this is the bitter truth.