Argonaut Scheduling and Appointments: This project supports basic patient and provider access to a provider's calendar and appointment requests, including APIs and guidance for searching and publishing a providers schedule andrequesting, cancelling or updating an appointment.
http://build.fhir.org/ig/argonautproject/scheduling/OperationDefinition-appointment-find-sprint.html
The sprint version of the appointment.$find operation has a system level operation listed, however this operation should only be resource-level.
URL: [base]/$find
URL: [base]/Appointment/$find