Spirit Blossom Lillia's horns from League of Legends, available as STL 3D printing files. The horns measure approximately 16.5cm in length and 8.5cm in height, which fits most printer beds without requiring any splitting.

To attach the horns, I would suggest gluing on a strip of worbla (or any similar thermoplastic), to slip under your wig cap. The base of the horns can then be secured to your forehead using spirit gum or pros-aide.

This listing is for the 3D printing files, but you can find the physical 3D printed parts under "3D Printed Kits".