To request a wheelchair-accessible vehicle from JetBlack, ask for it at booking, not at the curb, and give the exact pickup details and the access needs of the passenger, because a WAV has to be assigned to your trip in advance: a request made at booking can be confirmed in writing, while a request made on arrival may not be servable at all.

What to tell JetBlack when you book
Say that you need a wheelchair-accessible vehicle, give the exact pickup address and any access details that affect the pickup, such as steps, a narrow entrance, or a kerb that cannot be used, and say how many passengers and how much luggage are travelling. Confirm the vehicle type and the pickup plan in the same written confirmation as the fare, and tell dispatch promptly if the flight or the pickup time changes, since a WAV assignment is tied to your trip.
JetBlack does provide wheelchair-accessible vehicles. This page does not invent ramp or lift specifications, WAV models, or WAV prices, because those depend on the vehicle assigned to your trip: ask dispatch to confirm the details that matter to you in writing before travel.
Booking early, and what to check
Book as early as you can, especially for an airport pickup at a peak hour, and re-confirm the WAV request when you re-confirm the trip. If your plans change, tell dispatch at once rather than assuming the new time carries the same vehicle. Cancellation is free before confirmation, and $31 ($25 + $5 + $1) after confirmation, with gratuity not included and 20% suggested.