The architecture you are considering does seem a bit broken. ;-)
In general, a service needs a bundle which exports the service interface package and a bundle which publishes the service instance to the service registry. These bundles may be the same bundle or distinct bundles, but, if they are distinct, then the bundle that publishes the service must import the service interface package.
Bundles which are clients of the service must import the service interface package and obtain the service instance from the service registry.
Does this help? (If not, perhaps you could explain what you were hoping to achieve by loading a client class from within the service providing bundle's class loader.)