While you are on the site, in your browser find and click "Add to Home Screen" A CGN beaver app icon will then be created to your phone that is directly link to the site.
Note: This feature may not be available in some browsers.
Weaver makes something like this, but make sure you get ones tall enough to clear the scope bell or ocular.
EDIT: Also, while I have these and they're fine, I'm not too thrilled about the clasp and screws on one side of the ring top half. It's a PITA for leveling the reticle, because it torques the scope to one side as you ar snugging it down.