They are sold with factory grips.
Aftermarket sometimes have their own supplied or you cut out the original from your RH grip and re-use or get a cheap used one from a wrecker for $10-15. Most aftermarket grips for 1" bars are a bit bigger on the RHS to fit the cable throttle tube inside.
There are aftermarket ones with bigger cams which can increase the rate of throttle opening that racers use. As many of these parts a semi-standardized in size you may get options that fit but beware of very fast throttle openings as ithey may point you skywards or spin out on corners or cause traction issues with road surfaces.
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