The largest archive of Tram’s letters and writings is at the University of California, San Diego.
Tram Combs Papers, 1946 – 1964 (MSS 0123)

The University of Delaware has a great collection of Tram’s correspondence, mostly with John Brinnin. Brinnin was a good friend and important advocate of his poetry.
Tram Combs Correspondence

In the 1960s, Tram was working on a history of the post-war San Francisco poetry scene. He donated his papers related to this history to UC Berkeley.
Tram Combs papers : and other material, 1956-1973

UC Berkeley has most of Tram’s Correspondence with Lawrence Ferlinghetti.
Lawrence Ferlinghetti correspondence with Tram Combs, 1957-1964

I recently discovered the Social Networks and Archival Context (SNAC), which organizes archives of historical figures.
Tram Combs on SNAC

WorldCat lists 62 items for Tram.
Tram Combs on WorldCat

Tram Combs