No link; this is a "hidden" demo only available through your console (Kinect Central) like that Hitman Sniper Challenge demo. The link in your purchase history of the demo leads to a 404 page Ooops we couldn't find that page.
Also these Kinect Sports Gems (50G and 240msp each) have nothing to do with Kinect Sports Ultimate and are NOT part of the latter. You can still own and enjoy both if you wish.
Aren't the gems included with Kinect Sports, though? Or do the gems have different modes, levels, or something that differentiates themselves with the Kinect Sports' version?
I wouldn't pay 240msp just for useless gamerscore. Even if they were temporarily free like the 3-Point Challenge or the Ski Challenge, it's not worth the hassle if they're the same.