I found all eight volumes of the UK series New Poems and Selected Letters at a second hand bookstore in Somerville, MA over the course of about a year several years ago. Other than that, the only find I can recall is This is Not the Titanic, a poetry journal from '74 that I found for $2 at a used bookstore tucked back from the street about five doors down from where I lived in the fishing village of Stonington, CT back in '90-'92.