Trying to manage available date "inventory"

Hello! We have a team of about 25 and we sell retreat weekends. Each team member sends us their available weekends and we work with clients to find the right match. We need a way to track what weekends we have available and where. We might search weekends by team member or we might search by the state they are located in. The sales process can be long and so we would like to be able to mark a weekend as tentatively booked, booked, or available. Right now we are manually writing dates in like a text field but that keeps us from using the calendar view or running the kinds of reports we want. Any apps that you can think of or integrations to help us track this? Please note that clients are not self-booking, we only need a back end solution for this.