Correct Crank Bolt

Just to be sure, this is the replacement crank bolt I’d need for a KH or Impact right?

Are they widely available at bike stores, or are these different than bike crank bolts?

That bolt is M8 for Square Taper cranks. For ISIS there are two different crank bolts spec’d in the standard, m12 or m15. M15 seems to be more standard for bike cranks, while KH goes with M12 (if I remember correctly). As far as I know the Koxx Light is the only uni hub spec’d to M15, but that could easily be wrong.