Problem is not so much the bar end weights as it is the Bark busters or any accessory that needs to bolt into the bar itself. With the iso grip being longer than stock, the longer bushing/spacer is required so the accessory has a stop to hit against.
It is the Aussie firm's brand name Bark Busters from their use of metal hand protectors on offroad bikes when riding through scrub or brush. Since developed into a range for cold / rain protection for road bikes as well.
Mine are the Storms. If you go to the Barkbusters.net site and select Triumph Rocket 3. There are a few options. If you click on the Storm, it offers a single point bar end mount as the default option: