Jim,
You are correct that to get the blackjack chips you must either play the game or go to the poker room cage and buy them. It is very easy to buy them at the cage in the poker room. I have bought over 40 $.50 chips so far in three trips in addition to all the other denominations. This is only true at the McKellips location not the Indian Bend location. The reason there are so few $.50 chips on the blackjack tables is that they don't want the customers tipping with $.50 chips but rather want $1 tips. That was told to me by the floor manager.