There’s a post on this site on how to make the Octonauts Kwazii costume from scratch. Check it out if you haven’t read it yet.
As I wrote in that tutorial, what makes a costume is really the details. So for Kwazii’s costume, think about Kwazii’s ears and tails and the three freckles (?) on each cheek.
It’s not easy to buy an orange ear and tail costume so this is most likely one of those things you will have to make yourself.
If you’re looking for tutorials on making cats ears and tails, here are some of the best ones that I’ve found. Many of these tutorials use black material so change this with orange/yellow to make them look exactly like Kwazii. Also, don’t forget that Kwazii’s right ear has little rip (?) from his swashbuckling days.
Is it cold where you are during Halloween? Here’s a cat ear hat using fleece material. A little sewing skill needed
Fashionably Jamie gives a short tutorial on making cats ears and tails. Very simple but you can get the basic idea of how to make one yourself. Forward to 0:55 if you want to get straight to the tutorial.
Super easy cat tail tutorial
And here’s a different way to make the cat’s ears with a plastic cup, fur fabric and super glue!