I second the Centre Pompidou advice. In fact, you'll find plenty of them if you wander around the Les Halles shopping area i.e. near the fountain and the park. You can also trace the banks of the Seine river under the bridges, favorite spot of classical/jazz musicians and would really make for a good Parisian 'ambiance' picture. There's also the stairs of the Sacre Coeur in Montmarte teeming with tourist this time of year so you'll sure to find them there also. Until two months ago, i used to live just down this hill and after 5 years here, i still do at least 2X a week photo promenades in the area to sharpen 'street photography instincts' with a 4X5 Crown. Very tough and frustrating but like you, i find street performers very good subjects more than willing to be photographed. Some have become really close friends after i give them bw prints or our 'sessions'.