I don't think there is anything commercially available though I saw an article on the Rochester Institute of Technology website for a do-it-yourself project. The idea was to take a flash hot shoe with sync attachment, then add some circuitry so it worked in reverse. Basically the default state would be closed circuit, so attaching the camera flash would fire it, but then it would set to off. The shutter would open the circuit when it fired, and when the shutter started to close, the sync connection would change state and fire the flash. When I read through it, there was not an indication that it worked exactly like rear curtain sync, though it was enough delay to not work like a curtain opening sync. You might try searching through the DIY articles over at RIT.edu to see if they still have it posted.
There are some of the more expensive power packs that allow setting delayed flash. I think you might find that also on some monolights.
The only delay flash I know about is the Nikon SB-26, which has a delay setting on slave sync. Unfortunately you need another flash to go off to fire an SB-26 on delay. You could do that with a very low power initial flash, then use the SB-26 on delay slave sync to simulate rear curtain flash. While not the same thing, the effect is similar in the results.
Ciao!
Gordon Moat Photography
Is there a flash synch delay gizmo for leaf shutters? 
Linear Mode
