Are you looking for one-of-a-kind recordings that have never been commercially available? Do you want to set your research apart from other work? This may be one of the areas to investigate, it often takes more time, but the payoff can be new insights into artists through their unpublished work. These can be recordings someone made at home, live broadcasts rarely heard since the original broadcast, oral histories, or one of a kind recordings of live performances. Searching these types of resources will benefit from identifying specific artists and musical works you are interested in. Often the tool used for describing archival collections is a finding aid, covering use of finding aids is beyond the scope fo this guide, but following the link will give you a brief introduction to them.