Well i dont know a spell but there are natural ways to grow you eyelashes, such as:
Moisturising them( vaseline/ olive oil)
Eating fresh fruits and vegies containing Vitamin A,E and B.
Manage you're stress.
Moisturising you're eyelashes will also prevent them from bristling and falling out, eyelashes are the slowest growing hair on your body so patience is the key :)
Hope this helps