On my Mac the sampler instrument “Jazz Kit.exs” has been installed as part of the Jam Packs. The file is very old - creation date 2003. Did you previously have any Jam Packs installed for GarageBand? Then try to restore this file from an older backup. It should be found in the folder
/Library/Application Support/GarageBand/Instrument Library/Sampler/Sampler Instruments/Jazz Kit.exs
When I needed to reinstall the JamPacks I purchased MainStage 3. It installed all five JamPacks, so I could use them with GarageBand.
Have you already tried to reinstall or download the complete sound library in GarageBand?
Check out the menu "GarageBand > Sound Library". It will restore all sounds, that can be recovered, but will probably not restore the JamPacks, only the sounds and loops that are coming now with GarageBand.