Though not all seven are available, the Noble Collection's Harry Potter shop sells prop replicas of Tom Riddle's Diary, Slytherin's Locket, and Marvolo Gaunt's ring (and possibly Hufflepuff's cup and Ravenclaw's diadem, I can't remember).
at a music shop such as gould's .
Honeydukes sells candy in Harry Potter.
Madam Malkins
If you visit the Warner Brothers shop on WarnerBrothers.com, you can buy replicas of money seen in the Harry Potter films, but it's fairly expensive.
They started with selling a few products in Harry Potter and the Order of the Phoenix, but the real shop started in Harry Potter and the Half-Blood Prince.
Harry Potter costumes are fairly easy to come by. You can find them at online stores or at your nearest costume shop. Also check your closest Walmart or Target, as they usually carry Harry Potter costumes around Halloween time, at great prices.
In Harry Potter you find wizard books in the shop Flourish and Blotts in Diagon Alley.
You can buy them a Zonkos, a joke shop in Hogsmeade and Diagon Alley
yes there is
yes
Yes hamilys in London sells wands and other Harry potter stuff! :)
The best place to find these are in the Harry Potter world in Universal Studios Islands of Adventure. They have the candy shop, wand shop, joke shop you name it. If you can't go inside the park, outside of it is "Citywalk". One of the stores there sell almost everything that is available in Harry Potter world.