Old SMFShop versions used to have a button for Babylon, but I removed it in newer (SMF 1.1-supporting) versions.
I think the old code should still work:
In Themes/babylon/index.template.php, find:
<a href="', $scripturl, '?action=calendar">', ($settings['use_image_buttons'] ? '<img src="' . $settings['images_url'] . '/' . $context['user']['language'] . '/calendar.gif" alt="' . $txt['calendar24'] . '" style="margin: 2px 0;" border="0" />' : $txt['calendar24']), '</a>', $context['menu_separator'];
Add after:
//BEGIN Shop MOD 0.2 Code
echo "<a href='{$scripturl}?action=shop'>", ($settings['use_image_buttons'] ? "<img src='{$settings['images_url']}/{$context['user']['language']}/shop.gif' alt='Shop' style='margin: 2px 0;' border='0' />" : 'Shop'), "</a>{$context['menu_separator']}";
//END SHOP MOD
A "shop.gif" file is attached. Please upload it to Themes/babylon/images/english