I ask this because I got a Kanto starter but I didn't know if I could get a Hoenn one.
After you beat the Champion, you go to Silph Co. and Steven Stone will be there. He will give you a choice of Treeko, Torchic or Mudkip. You can also trade him a Forretress for his Beldum. On Wednesdays after National Dex, there is Hoenn sound on the radio, so you can get Hoenn Pokemon like that.