This is probably the link you want then:
http://old.mellanox.com/content/pages.php?pg=management_tools&menu_section=34
That's the older Mellanox website, prior to their recent refresh.
If the 2.7.1a version of mstflint doesn't do what you need, let me know. I downloaded most of the older flint versions several hours ago, as they're all actually on that same site... you just have to muck around with the path name to use the older version number and voila, they download. (previous version numbers can be found in the release notes)
Hope that helps. I used to use the InfiniHost III Ex cards a few years ago with RHEL/CentOS 6.0. They seemed fine for what I was doing.
Haven't used them recently though and I don't have any here to try stuff out on. Good luck though.
(note - edited for typo fix)