I haven't been yet (8 days ) so I don't know which shop it is in, but I know that they do have a replica of the time turner. However, they don't have the necklace yet (apparently it will be in stores some time in the future) they only have keychains.
Yes. In Dervish and Banges. It's not in the main store area, but in the side room, behind the register counter on a shelf. It is the full necklace and it comes in a glass display case. If I remember correctly I paid around $54 for it after tax.
They also sell it as a really cool keychain (full size) for about $10 I think. I got it for my friend and she just put it on a chain as she didn't want to spend the higher amount, but I would assume the $50 one is better quality!