I bought these a while back and they are my favourite Mario Kart toys so far. They are from Japan are packaged with a lolly. I find it amusing that it comes with an expiration date on it for the little lolly that comes with them.
When these are for sale, they come in a tray that holds 1 of each character so if you ever see these for sale in a shop, they probably have the whole set (or did originally).
You can tell which character is which by looking through the hole in the front of the box which shows a card covered in numbers, you then look at the back of the box and see which character the number matches with.
These cost me $12 each which was about the price they would have cost on ebay at the time. Pretty expensive set, but nicer than the dozens of Mario Kart DS toys.
If you buy these and want to keep the boxes like I did, open them from the bottom instead of tearing the tab on the top of the box. This way it will still look unopened. I opened one of them from the top and it looks really bad now. The rest all look fine.
On ebay there are similar looking sets to this which are really cheap but they are much smaller and not as nice and come with more characters than in this set.