Sorry to say then, but there's not a lot you can do. The Nomad Diablo does seem to be quite rare and i can't see many people being willing to trade for lower end cars. Apart from the obvious of keep checking, I would suggest saving a few credits, buy some decent cars wether you want them or not and then start a thread asking for the Nomad in exchange. I have one but would only take a Jaguar XJR9, Peugeot 905 or Nissan R89 for it.