You'll just have to buy them or find them used (which i found is quite hard).
If you are looking for the standard model wheel arches you are looking for wrong part, as the one you've post is for the Type-R/Type-S trim.
If you want the standard trims you should be looking for this instead:
Part Numbers: 74115-SMG-E50 & 74165-SMG-E50
Or are you doing a Type-R/Type-S conversion?
If you are looking for a conversion, when i've put the front type-r bumper on my 1.8 i bought the two new type-r wheel arches and a friend of mine cut all of them in half and merged them together.
Later when i've put the type-s side-skirts and rear bumper on i had to buy all the 4 new, so i can sell you the two i had before. As you can see from the pictures the one end has the flair for the type-r front bumper and the other end has the standard look. And the best part is that you don't notice the cut. Take a look at them https://imgur.com/a/e3jJO5g
I also got two standard for the back wheels.
Drop me a message with an offer if you are interested.