Where to find Hydra in GTA SA?

I'm curious, can you guide me on where exactly I can locate Hydra in Grand Theft Auto: San Andreas? I've been scouring the streets and haven't come across it yet. Is there a specific location or mission that unlocks its availability? And if so, could you please elaborate on the steps I need to take to acquire it? I'm really looking forward to adding this vehicle to my collection.