How can I see a list of products that I have set to outofstock through a custom field check box?

Question

You should be able to query ACF fields in the same way you query normal custom fields. With that in mind, you can do a simple meta_query to get a list of posts from the selected field

You can try the following:

$args = array(
    'post_type'  => 'products',
    'meta_query' => array(
        array(
            'key'     => 'stock',
            'value'   => '1',
            'compare' => 'IN',
        ),
    ),
);
$query = new WP_Query( $args );

EDIT

From comments, the correct value for the value parameter in the meta_query should be 1, not true