What sort of content are they? Threads, users, posts? If they're threads, you can find them using the batch thread tools in the control panel. Technically, you could do the same with users, though you would likely need to delete them (rather than setting them to "rejected").
Akismet doesn't match IPs, so I'm not sure which system you're referring to. If you mean StopForumSpam matches, then the options are split out by match type -- they just count the number of matches (IP, email, username) and take an action based on that. This is configurable in the spam options.
Akismet always sends matches to manual approval.