You need that jar that contains the package. To get it:
- go to http://search.maven.org
- Push Advanced search
- To the Classname, type "org.osgi.service.jdbc"
You will get a list of dependencies that contain the package. For example, the first one will be good for you: http://search.maven.org/#artifactdetails|org.ow2.spec.osgi|ow2-jdbc-service-1.0-spec|1.0.13|bundle
Btw.: The package originally comes from the OSGi enterprise spec (or compendium, do not remember). As much as I saw all of the OSGi spec packages are available in ow2 dependencies that separated logically.
In Karaf, there might be other ways to get the dependency you need but I did not use Karaf in the past.