I found a poem called "About My Tortured Friend, Peter." I read it and it reads almost exactly like a part I remember reading (re-reading only a week ago or so) in Post Office. Apparently the poem was published in "The Rooming House Madrigals: Early Selected Poems 1946-1966."
EDIT 1 (4:14PM): I figured it might just be easier to EDIT this thing than keep posting. I found a poem, "Empire of Coins," it's quite nice in a depressing kind of way. I imagine it was written earlier in the time span that's listed in the title.