Dicionário Ronga – Português written by Bento Sitoe and two co-authors. Despite its name it contains both, Changana and Ronga vocab (people often speak a mixture of the two dialects). Great book to look up vocabulary. Only drawback: It’s Ronga => Portuguese only, so you cannot lookup Portguese words to find the equivalent word in Changana.

Gramática da língua Ronga written by Cláudia Bachetti. I ate, drank and slept this book! Excellent and comprehensive book to study Changana grammar and language structure. Every section contains many sample phrases to explain the grammar. There is a helpful verblist Portuguese-Changana/Changana-Portguese at the end of the book.
Mahungu Lamanene (the good news). Of course the good old bible is also available in Changana. It is written in Tsonga, which is slightly different but still recognisable as Changana.
Nakaringana wa Nakaringana (once upon a time). Bilingual Changana-Portuguese, illustrated storybook with traditional stories from the Gaza province.
Antropologia written by P. Armando Ribeiro is an account of Changana history and culture, making many references to the Changana language.

Most of these books you can buy at Livreria Paulinas on Ave Eduardo Mondlane in Maputo.