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.
Yeah, Bukowski always goes fast, even the Ecco editions. The only Black Sparrow Buk I own is the Martinelli letters from D.G. Will's in La Jolla. Mr. Wills kindly gave me a poster of the same photo PhillyDave has with the text, "an early taste of death is not necessarily a bad thing." Classic portrait.
In Germany you don't find many Bukowski's in second-hand-stores, but there's a HUGE amount at German ebay on any given day at virtually no cost, so I guess the web is the place, where they fall of shelves.