I installed drupal 8 using the minimal install profile. For the admin pages I enabled the seven admin theme, but in the blocks admin screen I cannot find the Primary tabs and Secondary tabs blocks.
They are available under other names (I think one is called "Tabs") when you used the the minimal installation profile.
But you can import the blocks by entering the code of the files
into the Single config import located at
(this requires the config management module to be enabled)
I had the same problem, and I've just found the problem (bug).
In Drupal 8 (at least 8.3), there are 4 blocks ('Primary tabs', 'Secondary tabs', 'Page title', and 'Primary admin actions') that are all "install configs" within the standard install profile. In other words, they get created when you install drupal.
But they all have a dependency of the Seven theme. In other words, when you delete Seven, they are deleted. And they don't get re-created when you install Seven, because they aren't install configs of Seven, they're install configs of the Standard install profile.
Use Drush or Drupal console or the built-in Configuration Synchronisation to export your current configuration. Then copy the config files...
... into your config folder - which is probably
/sites/default/files/config_[hashcode]/sync/. Then do a config import (using one of those 3 tools above).