Helmet locks are usually matched to the ignition key of the bike they came on...I might have a couple...but, I'm not sure if I have a key for them...I'll check...
I know several people (me included) who use a gun cable lock for this.Like this:You can get them for free around here, at gun shows & stuff.I consider it a bonus that mine has the name of a major firearm manufacture on it -- Maybe it'll give someone thinking of taking it a moment of pause...Jeff