The ability to ‘purchase’ international numbers is dependent upon the policy of the country in question. Not all countries allow international numbers to be purchased, although many/most do.
Such numbers are price on application and in order to ascertain costs we first need to know:
a) the country in question
b) preferred city / area code(s)
c) whether or not the end client in question has a physical presence in the country in question (and so could produce if required, for example, company registration, a utility bill, etc. in their name)
Please note: there may be a charge for inbound calls to international number, dependent upon country and carrier.