Use Inventory Search. When you go into your dressup page, there's a search bar. Select "All Gaia" and type in the items you're looking for. Some items aren't in Inventory Search but what you can do is put on as many of the items you're looking to check as you can, then search the marketplace for the item not in Inventory Search. Preview it and click the button to see the item with what you have on in your dressup page.