http://gen.lib.rus.ec/ http://gen.lib.rus.ec/ is a pretty good source (also Russia-based). I'm not sure whether it covers all textbooks of the more obscure kind

http://gen.lib.rus.ec/ http://gen.lib.rus.ec/ is a pretty good source (also Russia-based). I'm not sure whether it covers all textbooks of the more obscure kind, e.g., the ones typically referred to as "monographs," but it has worked for graduate classes in the past.