I'm looking for a coping for the chimneypot that spins, to create air flow and stop the rain down the chimny

I am looking for a coping that spins to create an air flow, as the one I have just put on to prevent the rain falling down the chimney, just causes a back flow of smoke and the lounge fills with smoke. The chimney was swept in the summer. The problem with not having one on (as I have done over the years) is that the rain comes straight down the chimney and causes the soot to fall onto the fire in big lumps. I previously had an aluminium one but that blew off in bad gales and have not been able to find another . I live in Cornwall near Plymouth Thankyou