How about BA to Almaty in Kazakhstan and then Air Astana for the 90 min flight to Tashkent? No Avios or TPs with Air Astana, but it's one of the better airlines in Central Asia. With BA to Almaty you would get 140 TPs each way on a 767 with one of the older versions of CW. Don't expect much of a lounge experience at ALA however. I'm not sure if you would need a Kazakh visa if in transit and do not enter the country.