You can buy Portable Hole from Haris Pilton in Shattrath City during Wrath Classic Phase 4.
If you see Portable Hole on the Auction House selling for more than 3,000, don’t get scammed!
The 24-slot bag can be purchased directly from Haris Pilton located in Shattrath’s Lower City at 76, 31 for 3,000 gold.