There is no provision for a special election.
A curiousity is that there was such a provision at one time (this was the original succession law that Congress passed). If both the President and Vice President died, then the Senator Pro Tem or House Speaker (I can't remember which) would only act as president until a new election was held. The new election would have been held on the same basis (electoral college, etc.) as the regular elections were. The law simply copied the relevant parts of the Constitution.
