How many Champs in the Pool?

I am wondering about the odds of finding more of the same champ to make a Level 3 champ. How many champs are in the pool of each champ? Is it finite. When player dies, are their champs returned to the pool? I notice some players suddenly build Level 3 champs at the end, and i'm wondering if they are waiting for a player to die, then spend all their gold to fish out those champs they couldn't get before. And I'm guessing that if someone get a Level 3 champ midway there is no point in trying to get a second?