From what I understand, you have to use the appname when linking which is the slug that apple generates. So, for an app like like \'Guns and Weapons Encyclopedia\' the slug
Yes, there is. You can use the app ID to generate the link. You get the ID when you register an app in the iTunes portal.
You want a link like this:
http://itunes.apple.com/app/idAAAAAAAAA
Where, AAAAAAAAA is your app id.
AAAAAAAAA