Am not sure of what the issue was and how you resolved ... would be nice to know some particulars about your server ... like version of Moodle and Operating System ... but if you are talking about the plugins that come with Moodle core, not the addons, those are not made available as separate/downloadable plugins from the plugins site.
If you need to re-install something from core, you have to download the entire moodle package (that's why version info requested above) then copy the missing core plugins back into active core code. Needs to be from the same version of moodle you are running ... not lower and not higher.
'SoS', Ken
