Search in index.template.php :
// The [calendar]!
if ($context['allow_calendar'])
echo '<a href="', $scripturl, '?action=calendar"><img name="calendar" id="calendar" onmouseover="javascript:document.calendar.src=\'' . $settings['images_url'] . '/' . $context['user']['language'] . '/calendar_over.gif\'" onmouseout="javascript:document.calendar.src=\'' . $settings['images_url'] . '/' . $context['user']['language'] . '/calendar.gif\'" src="' . $settings['images_url'] . '/' . $context['user']['language'] . '/calendar.gif" alt="' . $txt['calendar24'] . '" style="margin: 0px 0;" border="0" /></a>';
Add before it:
//Begin SMFShop code
//loadLanguage("shop");
echo ($current_action == 'shop' || $context['browser']['is_ie4']) ? '<td class="maintab_active_' . $first . '"> </td>' : '' , '
<td valign="top" class="maintab_' , $current_action == 'shop' ? 'active_back' : 'back' , '">
<a href="', $scripturl, '?action=shop">Shop</a>
</td>' , $current_action == 'shop' ? '<td class="maintab_active_' . $last . '"> </td>' : '';
//END SMFShop code
But this Bloc theme is using images for buttons so i suggest you to make images for shop and instead of above code add this one:
// The [shop]!
if ($context['allow_shop'])
echo '<a href="', $scripturl, '?action=shop"><img name="shop" id="shop" onmouseover="javascript:document.shop.src=\'' . $settings['images_url'] . '/' . $context['user']['language'] . '/shop_over.gif\'" onmouseout="javascript:document.shop.src=\'' . $settings['images_url'] . '/' . $context['user']['language'] . '/shop.gif\'" src="' . $settings['images_url'] . '/' . $context['user']['language'] . '/shop.gif" alt="Shop'" style="margin: 0px 0;" border="0" /></a>';
So you gonna need shop_over.gif and shop.gif