With its latest release, Retrosheet has released games for fourteen complete Negro League seasons: 1936 - 1949. The middle twelve of these seasons, 1937 - 1948, encompass the entire time during which the Negro American League (NAL) has been recognized as a "major league" by Major League Baseball as well as the final 12 seasons in the 16-year history of the second Negro National League (NN2). SABR recognizes two additional NAL seasons as "major-league caliber": 1949, which is available here, and 1950.
You should readhere for some discussion of the data that are being made available by Retrosheet for Negro League games. Data can be downloadedhere.
1949 1948 1947 1946 1945 1944 1943 1942 1941 1940 1939 1938 1937 1936