You have some ability to filter these on the AS site, though not explicitly by fare class per se. A refundable economy fare is always going to be Y, and filtering by upgrade type and cross-referencing with the charts here can show you, for example, that any MVP first class upgrade fare will be either Y or S or that a GGU-upgradeable fare will be in K or higher. But if you don't mind calling in to book, you could use ITA Matrix to price out a specific bucket and then go from there.