The official website of the National Tourist Board is at http://www.madagascar-tourisme.com/

Their office can be found in Antananarivo :

 Lot IBG 29C Antsahavola – B.P. 1780

101 - Antananarivo

Telephone:  +261 20 22 661 15 /  +261 20 22 661 15

Several kiosks can be found in different places such as the Central Train Station.

Regional Tourism Boards also exist, they are in charge of the promotion of  each region.