After creating a new outbound connection for a certain calculation, it cannot be found under connections source list for a certain report.
The report is contained in a different component than the calculation needed to be added as source. Connectors do not penetrate multiple layers of components, therefore the report could only use the Inbound Connections of its parent component, which did not have a connection to the needed calculation.
Resolving the problem
Connectors need to be added to outer components as well. The solution is to add an Inbound Connection to the parent component of the report, that would point to an outbound connection of the needed calculation.