There is no current aftermarket pulley that is the stock size. There is discussion going on about having some made, but it has not yet happened. ASP makes the set of underdrives that most people are running. March may be offering an alternative soon, as a group buy was just executed with them. Not sure if they will be available for individual sale or not. Most likely a group buy would have be set up to get a stock sized pulley made.
Hope that helps.