I think you may be talking about the "Nova" special on the Lost Tribes of Israel? (Let me know if this is otherwise)
The Falasha is one of the groups mentioned on the PBS online exploration of the program.
The tribe you may be thinking of are the Lemba of S. Africa who do show the Cohen Modal Haplotype.
(The transcript of the show can be found here
http://www.pbs.org/wgbh/nova/transcr...706israel.html )