For anyone interested in buying single color Mungyo oil pastels online, i found the following websites:

Korea ~

http://global.gmarket.co.kr/item?goodscode=1847944072

https://www.coupang.com/vp/products/2156577487?itemId=3663043910&vendorItemId=71648465160&q=mungyo+oil+pastel&itemsCount=36&

searchId=60502bd1bf8045ec9988cf86e412928f&rank=12&isAddedCart=

https://ko.aliexpress.com/item/1005002877605433.html?spm=a2g0o.productlist.0.0.3d125ce5bDPEmk&algo_pvid=0ff1f8b4-2412-4e35-a39d-9c78ee429c2d&algo_exp_id=0ff1f8b4-2412-4e35-a39d-9c78ee429c2d-0 (Cheap international shipping)

http://item.gmarket.co.kr/Item?goodscode=1847944072

http://browse.gmarket.co.kr/search?keyword=%EB%AC%B8%EA%B5%90%EC%86%8C%ED%94%84%ED%8A%B8%EC%98%A4%EC%9D%BC%ED%8C%8C%EC%8A%A4%ED%85%94&s=1&f=c:200002418

http://itempage3.auction.co.kr/DetailView.aspx?itemno=B882081531

http://browse.auction.co.kr/search?keyword=mopv&s=4

https://www.11st.co.kr/products/2726096487?service_id=pcdn&utm_medium=%EA%B0%80%EA%B2%A9%EB%B9%84%EA%B5%90&utm_source=%EB%8B%A4%EB%82%98%EC%99%80_PC_PCS&utm_campaign=%EB%8B%A4%EB%82%98%EC%99%80pc_%EA%B0%80%EA%B2%A9%EB%B9%84%EA%B5%90%EA%B8%B0%EB%B3%B8&utm_term=

http://www.irehb.co.kr/m/product.html?branduid=38762

https://hwabang.net/product/%EB%AC%B8%EA%B5%90-%EC%95%84%ED%8B%B0%EC%8A%A4%ED%8A%B8-%EC%86%8C%ED%94%84%ED%8A%B8-%EC%98%A4%EC%9D%BC%ED%8C%8C%EC%8A%A4%ED%85%94-%EB%82%B1%EC%83%89-%EC%98%B5%EC%85%98%EC%84%A0%ED%83%9D/72366/category/118/display/1/

https://www.jiniart.net/FrontStore/iGoodsViewT1.phtml?iCategoryId=454&iGoodsId=0454_00020

https://search.shopping.naver.com/catalog/24064310764?query=mopv&NaPm=ct%3Dkqm4igcw%7Cci%3D65b0149d521577ed5f6d5bdbb52535b4580f0284%7Ctr%3Dslsl%7Csn%3D95694%7Chk%3D8eb006a1c79259c930201b889018ad546466c54a

Phillipines ~

https://shopee.ph/%E2%99%A5Mungyo%E2%99%A5-Gallery-Artists'-Soft-Oil-Pastel-Single-Color(201~220)-6-piece-i.438418069.11204434877

https://shopee.ph/%E2%99%A5Mungyo%E2%99%A5-Gallery-Artists'-Soft-Oil-Pastel-Single-Color(221~240)-6-piece-i.438418069.8355700243

https://shopee.ph/%E2%99%A5Mungyo%E2%99%A5-Gallery-Artists%27-Soft-Oil-Pastel-Single-Color(241~260)-6-piece-i.438418069.3689144337

https://shopee.ph/%E2%99%A5Mungyo%E2%99%A5-Gallery-Artists'-Soft-Oil-Pastel-Single-Color(261~272)-6-piece-i.438418069.2957139747

Cheapest 6 single-color pack, international shipping ~

http://aliexpress.com/item/1005002877605433.html?spm=a2g0o.productlist.0.0.3d125ce5bDPEmk&algo_pvid=0ff1f8b4-2412-4e35-a39d-9c78ee429c2d&algo_exp_id=0ff1f8b4-2412-4e35-a39d-9c78ee429c2d-0

If you're from another country, you can try using a package forwarding service or see if the store support international shipping. (Gmaket and Aliexpress support international shipping) Aliexpress shipping cost for small packages is a lot cheaper than most package forwarding services and Gmarket, but the items themselves costs a lot more, which means Aliexpress is a good option if you aren't buying in bulk and bad if you are)

You can read more about popular Korea shopping websites here: https://blog.trazy.com/top-korean-online-shopping-websites-you-should-know/ and here: https://www.trazy.com/experience/detail/order-korean-online-store-proxy-shopping

Good package forwarding services ~

https://koreanbuddy.com/

https://www.harum.io/

https://www.korgou.com/

https://www.paysable.com/

More: https://www.ivisitkorea.com/korean-buying-services/