I have the same issue. I tried opening at least 20 flower packs in different conditions: during the day, night, as a ghost, during a festival, after restarting the game. It never worked.
Someone also wrote that you can buy the death flower from the mysterious merchant, but he never has one.
Ditto on not getting a death flower from opening starter flower seed packets in the cemetery.
You can get a death flower from the Mysterious Rancher if you have Horse Ranch and befriend him.
As a ghost, I was able to deliver a death flower without ever having one in my possession. As soon as I took the quest from the Death Obsessed Lenore Member, the Obtain a Death Flower step was ticked off. And no, I checked several times, and there was no death flower in my possession. Not sure if this is a bug or working as intended.
I too was unable to get the death flower from the starter flower seed packet mentioned in the tool tip. It then occurred to me to try opening a Farmer's seed packet at the cemetery and that did work to get a death flower.
However, that 1) isn't what the tooltip says and 2) doesn't unlock until a sim has higher gardening skill (level 7 per Carl's Sims gardening guide, mine had maxed the skill so I had to check), so would make it harder to do.
Best regards,
Jennifer
