Instructions
Read the manual. Yes, it's painful, but sometimes it's the fastest route to answers. If the manual has gone the way of the missing game piece (as it often does), many companies now allow you save and print an electronic copy. Mattel -- a manufacturer of many of the Harry Potter games -- is particularly good about this. Check for contact information and its preferred method of submission requests. Some companies require you to call customer service. Others have printable request forms and still others (like Mattel) have online part ordering.
Scour the game manufacturer's website for precise instructions. Check its Site Map, its Contact Us page and its FAQ page for the best options. Don't forget to hunt like a bloodhound for that elusive customer service number. (Companies love to hide it!) Mattel has squirreled away its "Customer Service" and "Shop for Parts" links at the very bottom of its respective web pages. And while Mattel's online ordering system is good, parts to the various Harry Potter games seem to be only rarely available.
Check online for on- and off-line retailers who specialize in used games or game parts. Many manufacturers do not have replacement parts available for the older Harry Potter games. Used-game retailers, online auctions and gaming forums can be a far cheaper option than buying an entire new game from Mattel or Hasbro. Amazon.com, BarnesandNoble.com and Ebay.com are excellent starting points and are often the most secure sites from which to order used items. Other options include: Craigslist.org or Freecycle.org. Even the most obscure piece can often be found on these sites if you look long enough.
Go on a treasure hunt for your missing game pieces! Investigate thrift stores, resale shops, flea markets, pawn shops and garage sales. It's amazing what you can uncover if you take the time to peruse carefully. It also never hurts to ask friends --- real or Internet ones --- if they know anyone who would sell or trade for the piece you need.
Embrace the absurdity and make your own missing piece, if all other avenues fail! Substitute a small coin, toy or other object for the wayward piece, or unleash your creativity and craft your own. With a little forethought, you can devise a game piece that not only is better suited to you personally, but cooler too! Besides, every wizard and witch knows that they work best with tools they've crafted themselves.