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.
Here are dress, hat, and a necklace for a little (toddler) Witch. From storysims.
Forest fairy flowers in her hair, from . Visit the link to see all the colours.
The artist calls this a summoning rug. I wouldn’t have added it, because I don’t want anything satanic/demonic but it is a pentacle and seems to be right side up. So, here it is, from gremlins696.
From Margeh-75, a dramatic Witch dress. More for Halloween, but I like the jewel colours. Another, in an historical adventurer style, from Philosimy.