I've heard that most big automotive places should sell them, or agricultural dealers if you live in the sticks. Some say you should use special heat proof springs, but cheap ones you can replace as often as need be seem to be the way forward!
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball