AIRC the tank on my Abarth looks the same as the one on my previous 1.6, so I suspect they are commmon to all models. Might be worth trying ePER to check if the part number for the Abarth tank is the same as other models.
Sorry you couldn't find it. It is on ePER. The part number for all petrol models is 51722078, but there is an alternative part number for Stilos with diesel engines - 51727624.