I could be wrong, but I think I remember VMK having a calendar of events that would happen each month, and during October when lots of costumes were released, they would list the dates that certain costumes would be available on. That's something that MMK could use, it would benefit the staff by knowing when exactly to release what items, to avoid chaos like what happened in OVMK, and it would allow users to know when something is coming out.
If a player won't be able to get on during the day that item is released, they could set something up with a friend and have that person get it for them, and they could pay them back later.