Rule #3 on lemmy.ml says "No porn", but there's a lot that's considered NSFW that isn't porn. I'm not sure where they draw the line. I did see an instance lemmynsfw.com that might be a good choice.

If it's not de-federated from your instance, you can follow from your instance. If your instance does not federate with it, then you could just make an account there or another instance that federates with it.

There are NSFW Lemmy instances that do host porn. lemmynsfw.com springs to mind. You could just subscribe to a selection of their various communities.

For instance, searching for "boobs" brings up the boobs community from lemmynsfw. You can subscribe without having an account on that server. That is, unless you server has blocked lemmynsfw.

Edit: boobs example.