Converting Warlock Patrons

Demonology within Elsar is very different than Wizard of the Coast's Faerun and because of that warlocks aren't seen in as poor of a light in comparison. Necromancy within the warlock population is just as common as within the ranks of wizards and sorcerers, which is to say very rare. If you are a necromancer you can count any the Nine Divines or holy entity out as a patron.
All power for non-holy magic also comes from within you, so who or what is giving the power to a warlock? What happens to the roleplay aspect of a patron's contract? Keep in mind these are only a few examples that I chucked together to get you thinking along different lines. Mix, combine, and let me know! If you really really want to do something you feel I've crossed off the list then you present your ideas to me and we can figure out options to make it work.
Reskin time!

Archfey

While no Faewild exists in the world of Elsar the Astral Plane does! The plane is the embodiment of concepts and the biggest guns there aren't crisping your foes with fire or dicing them with steel. Instead trickery and obfuscation, changing the very mind of another being, hold the most sway. Spells and other magical effects that use wisdom or intelligence saves are using astral power.
You could be a shadow mage! After years of study you finally undertook a ritual to imbue yourself with astral energy, further attuning yourself to the powers of illusion and enchantment. Subtly you find yourself more likely to play mean spirited tricks on people.
You could be a resolution warlock! Through careful observation of a summoned golduck you are better able to impose your will over weaker beings. You hold contempt for those lacking commitment.
You could be a warlock! You do X and get Y related to ! You find yourself embodying more of the traits.

The Great Old One

Just because there are no demons readily accessible doesn't mean there aren't big bad things out in the world. In fact there are many ancient enemies floating around that would more than welcome a new minion. These represent a more classical patron as laid out in DND.
Drathlok the Blood Dancer has felt the rumblings of change and once again seeks to make his influence be known. While searching for profane knowledge you are captured and offered a deal. Accept his boon and be marked or become fodder for his craft.
Void Lord Faylot enslaved your family when you were a young child. Cruelty shaped your youth and you chose him over your pathetic parents. He has always offered power to those that are loyal...
The Thorns Forest is alive and angry. Its spirit feels the press of civilization hacking away at its flesh and seeks to use others to safeguard its border...
with could want you to help fulfill their in exchange for a promise of power!

Going Beyond

Don't feel the need to limit yourself from an RP standpoint, just pick an existing patron mechanic and pact then get to backstorying.

• Determine who your patron backstory target could be such as a mentor, master, school of magic, division within a pre-existing group, secret society, etc.
• Figure out what the patron wants out of the deal.
• Make something up to why you're beholden to their control for example it's because they've got blackmail, something you need or want, or any other multitude of motives.
• Describe how that control could be asserted should you anger them.