Peer review is either single or double blind. In both cases, the identity of the peer reviewers is not disclosed. The purpose behind this anonymity is to ensure that the review process is completely objective. Considering this, a request to disclose the reviewers' identity is not ethical as it defeats the very purpose of anonymous reviews.
However, if you strongly feel the need to get this reviewer's suggestions, you could write to the editor of the journal explaining the situation and asking what would be the best course of action. In all probability, the editor would not disclose the identity of the reviewer; however, you could request the editor to pass on your message to the reviewer. If the reviewer wishes, he/she might get in touch with you.