Andy Wallace dropped me this note this afternoon.

I sauntered down to the LOC with Norman Kennedy yesterday, and, while there, looked up "seek and you shall find." As I suspected it's an old spiritual. First printed version was in Jubilee and Plantation Songs, as sung by the Hampton Student Chorus, published by Ditson in 1887. There was a later Cabin and Plantation Songs, published in 1901, and also Religious Folk Songs of the Negro. So it was obviously in the repertoire of the black college groups that popularized so many of these sorts of songs.