Hi,
Unfortunately, the packages have not been formally tested and released for openacs 5.7 or openacs 5.6. Noone has been able to volunteer the time to test and tag them for release.
Some packages may have been released with a previous version of dotlrn.
That said, most of the packages on CVS HEAD will work on 5.6 or 5.7, you could also take the packages from the openacs-5-5-compat branch, as they should be forward compatible to the newer openacs.
I usually just get the packages from HEAD.