Bobby -- One classic in this genre is the Life and Journal of David Brainerd, missionary to the Indians, which is available online
here. Banner of Truth earlier this year published an edition of
The Diary and Journal of David Brainerd which is available for purchase
here.
One of the earliest Reformed missionary writings is by the French Huguenot minister Jean de Lery:
History of a Voyage to the Land of Brazil. He was sent by Coligny and Calvin to assist the first Protestant colony in the New World,
France Antarctique. The story is fascinating for its anthropological evaluation of a new culture, as well as its historical account of efforts to present the gospel to the Indians of Brazil. John Gillies,
The Martyrs of Guanabara, tells the story of the first Protestant martyrs for the faith in the New World, also at France Antarctique, who penned the first Protestant confession of faith in the New World, and the text, which is hard to find, is included therein.