Doing guro in 3d is a relatively hard thing in comparison to plain vanilla stuff.

But if you want it free you should use daz3d which is free and has more content than poser. and you just need to register on their website and take it for free. there are plenty of sites with pirated content.

Those 10gb renderotica torrents mentioned earlier are not that good since they are mostly old poser stuff but you can find some useful stuff there.

If you really want to do guro stuff, you will need Zbrush for morphs and photoshop to edit textures everything can be downloaded from torrents