Any replica is only illegal (to sell) if:
- It has a registered Trademark
- That trademark is used without permission.
So with cars I believe it may well be possible that licences are obtained to make a replica, and I bet any such licence include a clause denying the right to sell as an original, ie the replicacity must be disclosed.
I also imagine that to successfully sue (ie claim both legal expenses and some significant compensation) they would have to prove loss of sales of an original, which may not be easy to prove.