Poll the players on what prizebox should be sold next.

This doesn't even involve anything to do with changing the game itself. Just use any free, public polling site, post a link to the poll in General Discussion, let players choose from a list of every non-seasonal prizebox ever sold for a week, and then sell whatever box the players voted for the most. Every time a poll is completed, remove the chosen box from the list and do it again. The list slowly shrinks so that every box is sold once, and then the cycle restarts with a full list.

More boxes are sold at each sale, more players get what they want, everybody (except the people who really wanted really unpopular boxes) wins. Maybe the least voted for box could be sold alongside the most voted for.