Some ideas:
Do what
@Cuda Hunter suggests. Something like: Seeking 1970 Plymouth Cuda 340 in Plum Crazy Purple, VIN BS23H0B234583, last seen Rexburg, Idaho, circa 1990.
Your post with VIN and other data may get indexed by google, and searchable by people for years. Make sure you check months down the road for replies to your post.
Others may have ideas, too. And these are best shared publicly, out in the open for all of us to read. That is what this forum is for, to read about and learn from other people.
What about incentives?
If I owned this car, and I loved it, I may have little reason to contact you. So, consider stating what your goals are. For example, "I am looking for this vehicle, and will pay a competitive price for it. I want it, badly. And I'm prepared to pay for it."
What you may want to avoid saying is: "I'm looking for this vehicle, and if you will contact me, and tell me where you live, I will come steal it from you and you can file an insurance claim." Because the actual owners of this vehicle may choose to be cautious.