I would bet money that this is exceedingly rare. You'd probably have to have a 767 or larger for this to make sense, and only a tiny fraction of private jets are this large. And then it would still have to be extensively modified to be able to fit a car. Not saying it never happens, I'm sure there's some oil prince or oligarch with a 787 that has a garage, but "many cars like this" is likely a huge stretch. Happy to be proven wrong.

Now, do some people who buy cars like this have them shipped via cargo plane to wherever they're needed? That's slightly more believable, but I bet it's still very uncommon.