Kimchi / Mo-Chu Ka-roo?
You'd be better off trying to find the real thing.

Kochukaru is slightly sweeter and smokier than standard 'ground chilli' and simply substituting it will give you variable results to what your kimchi should traditionally taste like.

If you know what you're doing, and by that I mean you are able to know what Kimchi is meant to taste like and are able to tweak the amount of standard chilli powder you're using perhaps in addition to some sweet and/or smoked paprika you'd probably be able to replicate the flavour and taste of kochukaru in your kimchi.

If you're not at that level of ability (and I mean that with the greatest respect) then you're probably far better off trying to find kochukaru, perhaps at an alternative asian grocers or even online somewhere.