Special vehicles like the De’Leo Stiletto are unlocked through DLC content like Stones Unturned .

In Mafia III , you don’t "buy" cars in a traditional showroom sense; instead, you build a fleet through power, influence, and the strategic liberation of New Bordeaux. Your garage is a rolling arsenal of 1960s steel that grows as you dismantle Sal Marcano’s empire. 🏎️ The Fleet: How to Get Your Wheels

You cannot simply walk into a dealership with cash. Vehicles are earned through story progression and specific game mechanics: