www.herbalfire.com under Ethnobotanicals, "papaver somniferum". Fast shipment, great prices! I have grown them in the past, without much research (hence my post a few down on finding a grow guide) but they are relatively easy to grow, again, from my limited experience with them.
You can also get them from the grocery store I hear but they might not be "opium poppy". The best place is above. Its not illegal to sell the seeds, or even grow it. Its illegal when you score the pods.