Create custom template for blog
I don't think there is separate file for Blog content type. Because for Blog default node.tpl.php is called. If you want to create tpl file for blog, straight away copy file from node.tpl.php and create a tpl like node--blog.tpl.php.

And if you want to create page tpl for blog content type then you can create

page--blog.tpl.php

And you have to add some PHP code in template.php file in THEMENAME_preprocess_page() function

if( !empty($vars['node'])){
    $vars['theme_hook_suggestions'][] = 'page__'. $vars['node']-&gt;type;
  }