The Seven Deadly Sins can generate randomly in Gehennom. They are the only uniques that do this. There is no guarantee that you will encounter all of them, or even any of them.

Possibly make it so that you need to have committed the associated sin in order for them to spawn; if you have avoided being Satiated, Gluttony will never spawn, if you are celibate, Lust will never spawn, and so on.