You can just download a new package of phpBB3 ; http://www.phpbb.com/downloads/olympus.php , and upload the /styles/subsilver2/imageset/en/ and /styles/prosilver/imageset/en/ directory , those directory's contains the buttons.
Please remember this is not a support forum, for support you need to go the the 3.0.x style forums ; http://www.phpbb.com/community/viewforum.php?f=80