Based on this product's specifications, here are some alternatives and similar models
Chimney inner sleeve WADEX 125 mm diameter, model 125150160
Summary description:
WADEX chimney inner sleeve with 125 mm diameter (model 125150160) is a replacement/installation component designed for flue systems requiring a 125 mm bore. The sleeve provides an internal lining for chimneys and flues, ensuring a defined passage for exhaust gases and facilitating connection of flue pipes. Suitable for repairs, retrofits and new installations where a 125 mm internal sleeve is required.