Hello Bruce,
The first time I saw the jointed hair frog done was several years ago by an extremely talented tyer named Fabrizio Gajardoni, who was also featured (along with his remarkable patterns) in Paul Shmookler's Art Of Angling Journal.
His website, which features more of his excellent work is www.gajaflies.it, and it is certainly worth a look.
Regards,
Silverfish