UPDATE: FOUND - May 11, 2013, by YouTube user jeffdadude87.
The Wild Thornberrys is a 1998 TV pilot, created for Nickelodeon. The pilot aired twice on Nickelodeon (once on September 1, and once more in October during Nick's Big Help-a-Thon 5), and was never subsequently aired. It is the predecessor to the critically-acclaimed Nickelodeon TV show, The Wild Thornberrys.
The episode involves the Thornberrys attempting to record footage of an elusive black rhino in Kenya, in order to save their TV show from being cancelled. They eventually record the footage they need after narrowly avoiding a charging rhino, thus saving their show.
For reasons not-yet-known, this episode was not included on any DVD releases of The Wild Thornberrys, and as a result, it eventually faded into obscurity. However, on the 11th of May, 2013, YouTube user jeffdadude87 (who had previously recorded the entire Big Help-a-thon 5) uploaded a bootleg copy of the episode at the request of several users of the Lost Media Wiki. Thanks, Jeff!