The advanced on-board vehicles' resources have given birth to the Vehicular Cloud (VC) concept. The VC is an emerging paradigm where individual mobile vehicles can be both cloud users and service providers, it enables vehicles that have sufficient resources to act as mobile cloud servers and rent out them to other vehicles. However, and with the high mobility of vehicles, user vehicles need to discover vehicle providers, know their services, and request targeted services from them. In this paper, we propose a new protocol that enables user vehicles to discover and rent providers' services in VANet using public buses. Due to the predictability of time and space of these buses in urban scenarios, our protocol use them as cloud directories with which provider vehicles register and from which user vehicles discover all offered services. Hence, they hold a dynamic index of services' providers. We demonstrate the efficiency of our protocol, in terms of service discovery and consuming delays, by conducting an extensive set of simulation experiments using OMNet++ network simulator.