Actually you have it wrong. In fact all of his Pokemon from Kanto are with professor Oak. Also in a later episode he will have charizard.
^This was a question I asked and the user who answered said that Charizard is returning.
Also, if you didn't know, there was an episode where charizard was about to die of freezing. Luckily Ash revived his charizard and charizard itself regained its loyalty.