Name tags can be bought for hearts at the donation shop. Hearts are the donation currency that you pay real money for. http://www.ernya.com/shop-7.html
Or you can buy tags or hearts from users in the exchange. The tags are updated so the old ones are no longer available from the shop so you'll have to buy those from other people.
For future references, questions are more appropriate for the support forum. owo
~ If you didn't want to buy one right away though there is a pink name tag that comes from the marble next to your avatar, it's relatively rare I think though, also we occasionally get name tags from events :)