How to get many quality backlinks?

I'm in adult for about two years now and before that i was doing lots of mainstream.
One of the hardest things i noticed in the adult industry is how hard it is do generate lots of backlinks to a (new) adult website.

Unlike mainstream sites you can't just do lots of directory submissions because there aren't many (good) adult directories that don't require a link back.

Buying links is also hard because there aren't many quality adult sites that sell links.
Sure you can buy links but you usually end up on a PR3-4 website that has already over 100+ outbound links so it's actually worth shit getting listed on sites like this.

Doing link exchanges is good for getting your new site indexed but as far as i know it's of little value to increase your SERP rankings + it's also very time consuming.

Still sometimes i can see adult websites with over 10.000+ backlinks.

Now my question is, how do these webmasters do that?
Is there any special method i'm missing?

I'm actually pretty good at finding new niches, creating content, setting up new blogs, etc. but when it comes to building backlinks for an adult website, well i'm a total newbie

Any suggestions? Or "secret" tips for me?