The stun grenades were indeed something Gao Yang and his crew had on hand. When they were on the escort mission aboard the ship, each person carried a stun grenade with them, but there were only a few brought over. When buying grenades for the Skull Gang, they felt no need for stun grenades, which is why they didn't buy a large quantity.
Frey's face contorted with frustration as he muttered, "I only brought lethal grenades, damn it. I swapped my stun grenades for lethal ones and left the stun grenades with Rabbit."
Li Jinfang and Glolov, however, each took out a stun grenade. Glolov then said in a deep voice, "We now have four flashbangs. I think that's enough."
Gao Yang clapped his hands and said in a firm voice, "Alright, we'll use two on the third floor and keep two for the fourth floor. This time we're going in hard. Get ready."