Based on this product's specifications, here are some alternatives and similar models
Temperature sensor probe FF SONDA RT for RT-820 / RT-821 / RT-822 controllers (SONDA RT)
Summary description:
Replacement temperature sensor probe FF SONDA RT designed for use with RT-820, RT-821 and RT-822 controllers. The probe provides temperature measurement input for compatible regulator models and is intended for monitoring and control tasks in heating and temperature-regulated systems. Suitable for installation where OEM-compatible sensing is required.