I would think your best bet would be to thrift them or otherwise search out vintage sources. Last fall, I scored a mostly pants suit with trousers that drape like that, and I still have a favorite pair of lined wool gray Lands End trousers from the '80s(?) that also slouch. FWIW, I think is very much the cut that makes them drape instead of looking boxy. Yes, they have pleats, but they are really, REALLY huge at the thighs, then taper in significantly to the ankles to make them a petite length. Since they are both (probably) from the '80s, the waistbands hit at the real waist. With higher waists, it keeps the pleats from making the hips look too big, but for me, it impacts the comfort of the pants after a meal. I suppose one could try to size up, but I had to lose weight just to get into them.