Theres only a handful of MLP custom content for Sims4 (Why!? It's a 2014 game!!) and worst yet they are old/broken and some aren't available.
I found them using the Wayback machine and a Chinese & Russian websites.
Most noteworthy:
KaruDesigns - EG Mane 6 Clothes
TheUselessMedic - Mane 6 EA Recolors
I also decided to fix and make them compatible with Digitigrade feet for Furry mod users.
I also add some of my own stuff in and hopefully more (Not an artist) soon:
I made EA Hair recolors/re-mesh - Pastel-like (ex. Twilight Velvet, Flurry Heart, etc.)
I made Cutie marks (Tattoo, Lower Front) on both sides of the hips!
Made "LadyYunaChi > Lemonsimsa" clothes Standalone - no more default swatch
Merged similar recolors + other unknown/missing MLP creators stuff
(.packages are named in their respective creators and a .txt file detailing said creators.)
Currently, I only finished Twilight's Family Tree.
Important note: If any CC creators have an issue, feel free to contact me.
Please, comment first if there are any issues.