Quarq RIKEN 10R Power Meter GXP Crankset (50/34) - I know they have a 175 crankset but they also might have a 172.5 as well. Free FedEx shipping (ground). This is easily the best price I found when searching for my PM.
http://coolbreezecyclery.com/...t-50-34-191937-1.htm
http://coolbreezecyclery.com/...t-50-34-191937-1.htm