I think most people like the look of the cans unsuported hence no clamps. Myself like the cans to be clamped as i do a fair milage on my bike and have had the cambers crack due to the weight of the cans. Andy also has straps fitted for this reason (well his wobbled aroudn to much)

As for where you can get some if you want, there must be someone around that makes exhaust that would be able to make you some. Or try Swarbrick, they sell them in kit form so you can and drill your own.
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If I have to take the carbs off once more...