I upgraded my site to WordPress 3.5 and installed the Share This Plugin. The share link is showing on specific gallery items. I know that this didn’t use to be the case. So either its a new version of the plugin or new gallery setup in 3.5.
You might also be able to paste the code that you can find on the settings page into your attachment.php template.
Thanks Margarete!, I missed your reply somehow.
I tried the route of adding the code to a filter on the gallery shortcode. Which worked sort of. The attachment url link wasn’t passed however, so for facebook it linked to the page and not the item.
I may have to re-look at the attachment.php template as an option or better yet with your info on 3.5 update see if the share this links show up now on the gallery items.