The Prince and the Paupers - S1-E21
Continuity mistake: When the Monkees (excluding David) and Ludlow come out of the cupboard that they hid in when Wendy Forsythe came to visit, you can see some items in there on shelves and neatly stacked. When David (as Ludlow) and Michael accidentally open the door a bit later (thinking they're going into a different room), they get covered in the items as soon as they open the door. Plus some of the items that fall on them were not even in there before.
Answer: The Monkees TV series was very much a fantasy (this was the "groovy" psychedelic 60s, after all). Impossible things, such as items appearing out of nowhere, happened on their show without explanation all the time.
Jean G