I just installed the Kitaco Helmet Lock PN 564-0770100. There are two versions, this is the Black one, not the Chrome version.
I ordered from Webike.. http://japan.webike.net/products/21950424.html
I ordered last Wednesday and was at my door yesterday. 5 Days from Japan to Virginia for $12 shipping. Unbelievable!! They sell them on Ebay but they are cheaper if you order direct. Also, if you set up an account (supply email and password) they will give you a code for $6 off your first purchase.
Install was just removing two bolts, adding the bracket back behind and replacing the bolts. I realize someone with a metrick hex socket wrench can pull the two bolts off to get my helmet, but if they want my helmet, they can cut the strap and sew in new D-rings. It is like any helmet lock, it may stop only the walk by quick grab honest thief.
Very pleased, Looks OEM. Yamaha should have done something similar instead of the crazy rear seat hooks. I guess cost was a factor.
A couple photos of the helmet hanging. It rests neatly against the swingarm. It does not come as close to the rear peg as it appears on the photos. The rear peg will not chew up my helmet over time.