Thank you for your reply, MrsFlynn.
I ended up buying a bunch of seed packets and eventually got a few Lilies. Then I built a small greenhouse on my lot with a few planters and planted the Lilies, Snapdragons, Apples and Cherries I needed. I fertilized them with excellent quality fish then waited a few days. and I had my Lilies.
I think the reason Lilies never grow in Forgotten Grotto is because I have Seasons pack and Lilies only grow in summer?
Now all I need to figure out is why my spliced Apple Tree/Cherry Tree gives me Apples and Cherries, but no Pomegranate... It's in my greenhouse, so it shouldn't be affected by seasons.
I even caught an Angelfish trying to get large fish for fertilizing, and quickly put it in a fish bowl, so now I'll have an excellent quality Angelfish to combine with my Death Flower (to make Ambrosia)... if I can grow the Pomegranate and Orchid, splice them and grow an actual Death Flower. We shall see.