Bahn.de? You can also do travel planning for the whole of Europe though you cannot book non-DB trains through that website.

The brainless should not be in banking -- Willem Buiter

Also Köln-Warsaw. If you have a hard time getting a ticket out of Paris, driving to one of these and then taking the train might work. You can book the night train (but not always the train from Paris) on bahn.de; I checked several of them, and they even have some discount rates for couchettes left; I doubt that's what you're looking for, but it's an indication that not too many people are trying this option.