This is a link to a thread showing 2 such commemorative medals established and bestowed under the authority of the fleet commander. http://gmic.co.uk/index.php/topic/55177-fleet-commanders-awarding-commemorative-medals/ Commemorative "badges" are not regulated by the Defence Ministry and are tolerated for wear on the uniform. Even if a commemorative "badge" is in the form of a medal and hangs from a ribbon like the two you'll see at the thread above, calling them "commemorative badges" removes any and all restrictions. Like I mentioned before, air force and navy commanders have been going nuts over this loophole and are issuing commemorative pieces like there's no tomorrow! Squadron, base, wing, division, brigade anniversaries... Name it.
As for using already existing awards like the "Long Cruise" badge, hey, its MUCH cheaper than having a firm design and produce a new award, especially when your own unit supply has boxes full of them. But I would guess the silver ones were made especially at the request of a pretty financially well off commander who really wanted his deserving personnel to have something special. That, or a Russian firm is selling them as souvenirs to tourists, that wouldn't surprise me either, commemoratives can be purchased with ease, they'll even sign and officially stamp the award document for you!!