If you want them for free then your choice is fairly limited. You can get some do follow links on related adult sites by exchanging or try some forums, but add some valuable posts first.
You could build some blogs on blogger, tumblr or other free platforms, but obviously, you should get them on a paid hosting if you can afford it, because you can totally control them.
I have created thirty small blogs for link proposes, but I still update them once in a while and it costs me over $50 a month to maintain them, but it is definitely worth it judging by the SEO results and the profits.