I have to admit its quite difficult to find a professional proofreader for Korean Language on internet, because most of them are hiding behind marketplace.
You may find a good proofreader for this language on many translation or interpreter marketplace, but not on their personal website. Don't they know how to create a website for themselves? Hehe
Anyway, here I wanna share a gig offering this service on Fiverr. This gig, the seller is giving you professional Korean proofread service at a really cheap rate. 500 words for only USD5, where else you can find this great deal?