django custom command not found

The directory structure in your answer is a little ambiguous; when placing the files as follows django should be able to find your command:

project/ # in your question this would be 'application'
    manage.py
    blog/
        __init__.py
        models.py
        management/
            __init__.py
            commands/
                __init__.py
                myapp_task.py
        views.py

Furthermore, you’ll need to enable your app in your settings.py:

INSTALLED_APPS = (
    'django.contrib.auth',
    'django.contrib.admin',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.sites',
    'blog', # <= your app here ...
)