This is the only item I know of that describes black troops in Montgomery, AL-

"At Montgomery, the capital of the confederacy, negroes were being drilled and armed for military duty."

-William Wells Brown, The Negro in the American Rebellion, p.59
http://quod.lib.umich.edu/m/moa/aby0202.0001.001/75?rgn=pages;view=image;q1=montgomery

There is no date, but Montgomery is described as the "capital of the confederacy" (1861). As if it were a militia company of free blacks. But I've never heard of such a company and there were not enough free blacks in Montgomery to form a company.