The problem of flash data dissemination refers to spreading dynamically-created medium-sized data to all members of a large group of users. In this paper, we explore a solution to the problem of flash data dissemination in unstructured P2P networks and propose a gossip-based protocol, termed Catalogue-Gossip. Our protocol alleviates the shortcomings of prior gossip-based dissemination approaches through the introduction of an efficient catalogue exchange scheme that helps reduce unnecessary interactions among nodes in the unstructured network. We provide deterministic guarantees for the termination of the protocol and suggest optimizations concerning the order with which pieces of flash data are assembled at receiving peers. Experimental results show that Catalogue-Gossip is significantly more efficient than existing solutions when it comes to delivery of flash data.