If you have a Laboratory, have a Vial of Queenly Attar (obtained from Arbor), and don't want to be at the mercy of the fickle RNG gods...

<a rel="nofollow" class="external free" href="https://fallenlondon.wiki/wiki/Study_the_properties_of_Attar">https://fallenlondon.wiki/wiki/Study_the_properties_of_Attar</a>

Finish the research, get one Night Whisper guaranteed.