You have a few options, none of which may be entirely satisfactory. You can use the Users Import/Export plugin to export your list of reviewers, which would give you an XML file with all reviewer information (in which case you would need to clean it up, and probably convert it into something a little more useful); you could enrol them as Journal Managers, in which case they would be able to see the reviewers, but would also have access to all JM configuration options; hrm, and maybe that's it by default.
It's probably possible to write a Book Reviews plugin that would allow editors to view the list of Reviewers (and associated interests) and solicit a book review via email. Do you have any development resources on hand? We could offer some suggestions as to how to develop such a thing. If not, I can add it as a feature request (and I think it's a good one), but I can't guarantee how fast we'd be able to get to it.