carnavalesco is a website publishing news, pictures, and videos for the whole year on this page.

só samba (translatable as 'only samba') publishes news about carnival, and has sections dedicated to many samba schools in rio on this page.

while in rio during the carnival period, the magazine to look for is rio samba and carnaval, published in english and portuguese, it is distributed for free at the sambódromo, at the airport, in some hotels, and is some tour agencies.  

to watch in real time some of the main carnival event, the website tvgrio shares lots of programming via this link.