DK,
search ASA test prep on amazon.co.uk/com if you haven't come across it.
other books, well, plenty in pdf format off FAA website, plus recommend (second hand cheaper) commercial/instrument training manual (Jepp).
It's OK to get some of the ASA test prep few years dated (except maybe CFI stuff due to new questions) as not much changes there, 'as new' condition etc. You're probably away from this damn cold/crap weather place by now. Just FYI.