Brownells, Midway, even Amazon- but I would check with Ruger first for suggestions. Mounting a 50mm scope will be difficult due to lack of clearance- a 56mm will be VERY difficult. And not that you asked, but probably too much glass for a rifle that is not a high precision target rifle.
Should serve you well. You will need mounts and rings.
You must contact Bushnell to find out.
Contact Bushnell
Bushnell is a well-known manufacturer of hunting and outdoor equipment. Bushnell Elite is Bushnell's line of optical equipment, and includes rifle scopes and binoculars.
Adjustable Objective
There are lots of companies to make rifle scopes with well design and proper zoom options. Nikon scopes are classified as the greatest in looking optics.
100-400 or so
One can purchase rifle scope mounts from websites like Optics Planet, Cabelas, Amazon, Scope Mounts, Airgun Depot, eBay, Talley Manufacturing and Jmecks Scope Mounts.
A Bushnell banner is a type of optic scope from the Bushnell company. The uses of this would be for target shooting or hunting purposes. The Bushnell banner would be mounted on a rifle and used to identify and take down game or in target shooting applications.
100-400 USD or so
75-100
5-80 usd