I've been following the walkthrough, but now I need some diseased dead tissue and can't find the cemetery (already hired the butchers and found their bodies). Anyone know how to get there?

From the place where you hired the butchers (Ospina's place) it's pretty much directly east to the cemetary gate, and somewhere on the back wall is what you are looking for, shoudl be visible from the entrance. It's labelled on the map, Laska's lodge is in it.

If I recall correctly, you'll need a fair chunk of bribe money or must fight the guards.

Follow the road to the cemetary (bottom right corner of the map) and you will see a bonfire from the entrance. There will be three guards standing beside a burning body. Now, I am not sure how I did this, but the second time I tried (I was killed the first time), I shot at them with my gun while going backward and the screen went black. I found myself in front of Saburov, who told me that I had 10 minutes to go back to the cemetary before he sends other guards.

I do not know whether it's because I ran away from them or because I attacked them, but I found that this is the easiest outcome, unless you want to pay 10 000 coins.

It's because you ran away.