In the story "The Most Dangerous Game," where does the line 'black bearded' come in. I can't find it in the story.

This is a good question.  These words, "black bearded" come into the story when Rainsford finally gets to shore onto the island.  As he proceeds to the house on the island and knocks on the doors, the door opens and he sees a huge man, Ivan.  Here is his description of him:

The first thing Rainsford's eyes discerned was the largest man Rainsford had ever seen--a gigantic creature, solidly made and black bearded to the waist. In his hand the man held a long-barreled revolver, and he was pointing it straight at Rainsford's heart.

We can say that this is Rainsford's first encounter with the inhabitants of the island.  His first interaction does not bode well.  To be sure, General Zaroff, at first, seems congenial and kind, but Rainsford will quickly find out that General Zaroff and Ivan are not good hosts.  They are blood-thirsty and they will seek to hunt him in a game of wits.  In the end, Rainsford decides to go on the offensive in a game where he will have to kill or be killed. Fortunately for Rainsford, he wins.