From what I understand, the flexbait has a flexible core, made out of rubber or some other type of material. The plug itself has a bunch of slits all along the plug. With all the slits and the rubber core, the bait can move side to side quite easily. It's like those wooden toy snakes, if you've ever seen one. Finding a flexbait would probably be pretty tough. Rob got his from Eric's Tackle in Ventura. He had one on the shelf. You might try giving him a call, he might be able to at least point you in the right direction.
-Brian