always at the organic ! and what they have that is delicious, is beluga lentils - tiny black ones that are great to serve cold as a salad with all sorts of veggies and feta cheese.
Lulu stock them - I regularly see them at the Al Barsha store. The brand is Gourmet Merchant I think and they have several different varieties. Cost about AED 25.
I've often found puy lentils at the organic store. They are either in the back, near to the toy area and the butcher, in with the grains or in the bulk area by the bakery. I also occasionally find them at Choitrams on Al Wasl by Safa park.