Nothing is free in life! With the exception of the Limousines for your Genestealer Cult. You can equip your Coven by up to 3 Limo for no point cost... Old armies lists charms!
Unfortunatly, Citadel miniatures never provided its range of this type of vehicle. Only one advice to help you : "You can use 1/43 die cast models..."
If you have some difficulties to find these die cast vehicles, you can check the web site of Wargame Exclusive. They purpose a sumptuous Armored Coven Limo on Antigrav. Very inspired by the illustration in the old army list, what more could you ask for?