The John M. Olin Library at the University of Washington in St. Louis, Missouri, has a couple different Plath collections. They have a Hughes Collections as well as the papers of Lee Anderson. Lee Anderson met Plath and Hughes around 1958, and recorded both poets reading their poems during their time in Northampton and Boston.
The Lee Anderson Papers (finding aid here) contains the following:
Plath's autograph in an autograph book and this quote, "Yet, shrined on her shelf, the grisly visage endured", from her poem "The Lady and the Earthenware Head" dated 15 April, 1958, and two letters, dated 27 April, 1958 and 18 February, 1959. The Lee Anderson Papers also includes a number of typescripts of Plath's poems. These are:
- November graveyard [poem]. Ts, with corrections, 1p., [1958]. (27 April 1958).
- Spinster [poem]. Ts [carbon], 1p., [1958]. (27 April 1958).
- On the plethora of dryads [poem]. Ts, 2pp., [1958]. (27 April 1958).
- On the difficulty of conjuring up a dryad [poem]. Ts, 2pp., [1958]. (27 April 1958).
- Battle-scene from the comic operatic fantasy "The Seafarer "[poem]. Ts, 1p., [1958]. (27 April 1958).
- Sow [poem]. Ts, 2pp., [1958]. (27 April 1958).
- All the dead dears [poem]. Ts, 1p., [1958]. (27 April 1958).
- The earthenware head [poem]. Ts [carbon], 1p., [1958]. (27 April 1958).
- On the decline of oracles [poem]. Ts [carbon], 2pp., [1958]. (27 April 1958).
- Departure of the ghost [poem]. Ts [carbon], 1p., [1958]. (27 April 1958).
- The disquieting muse [poem]. Ts [carbon], 2pp., [1958]. (27 April 1958).
- Poem for Paul Klee's [poem]. Ts [carbon], 1pp., [1958]. (27 April 1958).
- Sylvia Plath to Olwyn Hughes n.d.: June 30 (Monday). 1 item (1p.): ALS
Autograph letter signed, from Sylvia Plath to Olwyn Hughes, describing their recent activities at Smith, and discussing their hopes and plans for writing in the next few years. - Ted Hughes to Graham Ackroyd n.d. 1 item (1 p.): ALS
Autograph letter signed, from Ted Hughes to Graham Ackroyd, inviting him to visit them in London when he is there. - Sylvia Plath to Olwyn Hughes n.d. 1 item (1 p.): ALS
Autograph letter signed, from Sylvia Plath to Olwyn Hughes, describing their moving-in activities; ms. note from Ted Hughes appended to letter from Sylvia Plath to Olwyn Hughes. - Sylvia Plath and Ted Hughes to Olwyn Hughes n.d. 1 item (1 p.): ACS
Autograph card signed, from Sylvia Plath and Ted Hughes to Olwyn Hughes, describing winter in Boston. - Sylvia Plath to Olwyn Hughes n.d. 1 item (1 p.): ALS
Autograph letter signed, from Sylvia Plath to Olwyn Hughes, discussing her current work and commenting on their life in America.
The special collections library web site is here.