While this seems that is should be obvious, searching on Google for Carnaval Tickets or Where to buy Carnaval Tickets? or similar yields a whole bunch of websites, none of them seem official and with widely different prices, a factor of 2X or so.
Is there an official site to buy tickets from? Or a place with at least an official reference price?
Are they reliable online vendors? While I would reasonably use a reputable third-party to save money, I want to make sure to get an actual reservation. Also, I will not be in Brazil until 2 days before Carnaval, so it has to be purchasable online, either print-at-home or pickup on location up to 24 hours before the event.