SimsService has a Witch costume, a hat and sweater mainly. Also a cat hat, which was more Halloween fun than real Witch. I also found a necklace with a dragon on one of her other creations from the same cartoon series.
A nature Witch hat, dryad hair and mask and Medusa hair from feralpoodles. You may not thing you would ever use Medusa hair with a Sim, but now that you know its there, the temptation will be there.
Witch hat by CowPlant’s Cake.
This looks pretty. I haven’t loaded it yet but I like the image preview. Sparkly Witch Set with a hat, gown and jewwellery from HeavenSent418.
Colourful Witch hat with two versions, by Kalewa-a.