This one can be tough if you intend to get it legit. The best way is to stick to UMK3 because if you can find someone online, they are usually playing UMK3. Learn a combo or two with a favorite character and go for it.
That or you can just ask the person you are fighting to let you flawless them. You only need to flawless one ROUND not the entire Match.
Good luck, you can do it!