Based on this product's specifications, here are some alternatives and similar models
Seat backrest for sleds Prosperplast ISEAT1 — compatible with Bullet, Bullet Control, Tatra (blue)
Summary description:
Prosperplast ISEAT1 is a removable backrest designed for use with Bullet, Bullet Control and Tatra sled models. The blue backrest provides upright support for a seated passenger, improving comfort and stability on family sleds. It is intended as an accessory replacement or upgrade for winter recreational sledding and short-distance transport on snow.