Here is one from Port Royal, collected in 1861, before most slaves were freed. The type of song that you ask for, as someone has already noted, would be very rare if it exists at all. Oblique references in religious songs about the freedom in Heaven to come are the closest to what you request. Songs like the "Drinking Gourd" are very doubtfully of the period and have much myth attached.
I have titled this one so that it can be indexed.

Lyr. Add: PRAISE AND THANKS!

Oh, praise an' tanks! De Lord has come
To set de people free;
An' massa tink it day ob doom,
An' we ob jubilee.
De Lord dat heap de Red Sea waves
He jus' as 'trong as den;
He say de word: we las' night slaves;
To-day, de Lord's freemen.
We'll hab de rice an' corn:
Oh. nebber you fear, if nebber you hear
De driver blow his horn.

Collected by John Greenleaf Whittier at Port Royal, 1861, "At Port Royal, 1861," pp. 244-245, Atlantic Monthly, 9 (Feb. 1862). Sung by Negro boatmen. Reprinted in Epstein, Dena J., 1977, "Sinful Tunes and Spirituals," pp. 257-258.
(Added to Spirituals Permathread)