actually Document put out some of the small group Fisks a while ago - also, the regular Fisks (meaning the actual-sized group) recorded for Folkways, I think it was, at some point, in the 1950s, maybe.
And let me point out that Seroff is good, but the definitive book on the Fisk Jubilee Singers was written by Andrew Ward, who just happens to be my brother-in-law.
it's a terrific book and should be read.