I agree with malasuerte that the supplier is within their rights to refuse to provide you this documentation, and instead to counter-offer that it can be viewed during an on-site visit.
HOWEVER, with that being said, it would definitely raise some red flags for me (especially if they are located at a sufficient distance that an on-site visit is unlikely). What is it that they are trying to conceal? Are they registered with ISO/IATF?