There's a room dedicated to Poussin's work at the National here in London, have you been? I reckon you'd enjoy it, but the wardens stop anyone taking photo's, even without flash.
In Paris at the Louvre there's also a room dedicated to Poussin's work, IIRC there are 8 paintings hanging there, and no one looked when I took pictures without flash.
I took pictures of Le Bergers with flash at the Louvre, as a result the right of the picture was obscured.
On the subject of Poussin the National Gallery of Scotland has his paintings of the Seven Sacraments