As far as I can see, in every single book of the original Hardy Boys series the brothers get kidnapped in chapter 19. From a cursory glance, I can tell that this applies to The Hooded Hawk Mystery, The Mystery of the Chinese Junk, The Yellow Feather Mystery, The Firebird Rocket, The House on the Cliff, and The Secret of Skull Mountain.
For this question, the "classic" series means the fifty-eight hardcover books published from 1972 to 1979, and their companion novel The Hardy Boys Detective Handbook. A book only counts as them not being kidnapped if neither of the brothers was kidnapped.
Are there any books in the classic series that they do not get kidnapped in chapter 19?