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Bellagio is the most likely place to see these players. Of course, if you want to actually take on the pros, you'll have to be prepared to sit down with a pretty significant bankroll, willing to fade high stakes. We'd guesstimate that your minimum bankroll should be in the $20,000-$25,000 range.
If you just want to star watch, look for any major poker tournament, such as the World Series of Poker or the World Poker Tour, and show up at one of those events. Odds are you'll see all the pros, along with some up-and-comers whom you can later claim to have seen before they made it big.