If the examples given for Archfey and Great Old Ones that can serve as Warlock Patrons (and as found in the Sword Coast Adventurers Guide) don’t work for you, you can always go with Queen Radanthe, ruler of the Dryad Realm of Aloushe within the heart of the King’s Forest, in Cormyr.
What are some of the things Radanthe would want a Warlock to do? And what secrets will she reveal to a Warlock she makes a pact with?
1. Radanthe desires for Warlocks to do battle with all beings that hunt, capture or slay fey.
2. She wishes to see all fey set free that are currently imprisoned, being experimented on, or are enslaved–especially fey that are being magically compelled to act against their will.
3. Radanthe desires humans to know about fey in general. Because she despises tales of treachery or doom that falsely identify fey as the culprits, as well as stories that don’t hew to the truth of what fey are and are not, she expects Warlocks to speak truth to such stories whenever they are overheard.
4. Because the Sundering realigned the planar cosmology of the Forgotten Realms, and because the Sundering largely shored up planar boundaries, many creatures from the Feywild have become stuck in the Realms. While any fey creature seeking to return to the Feywild can do so by traveling to Aloushe and similar fey realms, and from their cross over to the Feywild, it’s also true that places like Aloushe are isolated, the journey to them is difficult, and not all fey know where the places in the Realms ruled over by fey are located.
5. Thus, Radanthe will unveil the existence of Fey Crossroads (see the Third Edition sourcebook Magic of Faerûn) to Warlocks she has come to trust, as well as the general location of fey in need, so Warlocks and their allies can accomplish two things.
6. First, they can explore the Crossroads and scour them of any dangers that occupy them, and help any beings lost in the Crossroads to find their way to safety. After all, planar realignments are good for shifting creatures against their will into the spaces between worlds.
7. Second, a Warlock and their companions can locate lost or isolated fey in the Realms, and then guide them back through the Crossroads to Aloushe or a similar fey realm, so the lost fey can either join the Dryad Realm or depart for the Feywild.
8. Because Radanthe’s greatest fear is that humans will come to see **all** fey as evil, and so decide to slay fey wherever they are encountered, she will want to know the disposition and doings of fey beasts, and all other terrors associated with fey that humans believe have may have found their way into the Realms from the Feywild.
9. This includes the trolls that have come to plague the region of the King’s Forest centered around Waymoot. Combat-minded Warlocks will be the first to receive news from Radanthe about trolls and other terrors that need taking care of. (See Map below)
10. Some beasts will need to be led deeper into woodlands where humans rarely go (such as the Hullack Forest, or the deepest part of Hermit’s Wood in southeastern Cormyr), the better to preserve those woodlands and keep humans from despoiling them.
11. In rare cases these creatures will cross back over to the Feywild naturally, provided they are led deep enough into the woodlands. Player character Warlocks will have learned from Radanthe that they have gone far enough into the woods when their shadows no longer stand opposite any light source, but instead always point away from the deep darkness of the wood and in the direction of safety.
Tip of the hat to Aaron Dodson over at the Forgotten Realms Archives group on Facebook for nudging these ideas out of me.