At BA at outstations, the TRC/TRM normally hands in any items left onboard that are found during any security check/search or during cabin cleaning. At an outstation any items found onboard would be handed to BA's appointed baggage handling team (the staff at the carousels where you would open up a file if your baggage is delayed or damaged). If the TRC has a seat number he/she will provide it to the baggage handling team who would try and locate you if you have provided any contact details or if you are an Executive Club member. The TRC would not normally hand any items left onboard to the airport's lost and found. You would be best to contact BA's baggage handling agent at ZRH.