Have you tried tapping your finger on it and holding it there for a few seconds? I don't have an email with an audio file handy so I can't test at the moment but with other attachments that brings up a menu where "Copy" is one of the options. Then you could paste it into a text to send off.
EDIT: just tested this and holding down a finger on the audio file does bring up a menu but "Copy" is not one of the options. Sorry!