borrow from local library? Here in Seattle King County Library does interlibrary loan - they got me a book from Australia once. Had to give back of course - sigh.
Local college engineering type library?
If you buy direct do you have to have a membership like you would with NFPA IEEE or EPRI to get discount?
I would also check with an email to bsi what the latest standards are and any amendments if any as some online retaillers are an amendment or 2 behind.
I would imagine you could also buy from the US BSI office as wecan buy over here from the UK BSI office.