Caslon 540 is closest, with less contrast than Big Caslon. Adobe Caslon has less than 540. My Williams Caslon Text http://www.fontbureau.com/fonts/WilliamsCaslonText/ has still less. The bold on mine, which has higher contrast than the regular, will work at bigger than text sizes.

¶ Apart from the solid Adobe Caslon, you can try:
Caslon Classico by Franko Luin
Kings Caslon (Dalton Maag) by Marc Weymann, Ron Carpenter

Thanks :)