To unlock the secret trophy shop, successfully complete three playthroughs of the game to complete the full story. Then, find the Strange Resistance Woman in the Resistance Camp. Talk to her to see a large list of options. Select the "Request unlocking you-know-what" option at the bottom of the list to display the trophies list. Each trophy is numbered, so you will have to check the description to view which trophy you are buying. The prices are 50,000 for Bronze trophies, 100,000 for Silver trophies, and 200,000 for Gold trophies. They are very expensive, and buying them all can be extremely costly, but this is an alternate method to getting the Platinum trophy.