Oxymorons are figures of speech that are contradictory, antithetical ... opposing ... and are at odds when grouped together. To understand it better ... it is a phrase that combines two words that seem in conflict ... or incompatible with each other.
The classic example of an oxymoron is DEAFENING SILENCE. The night is silent or quiet... and you can almost hear the pin drop. How could you possibly combine silence with deafening? Meron bang " nakakabinging katahimikan" in real life? The two words are "in opposition" to each other ... no question about it.
But there was a time in my life when I agreed I could use deafening to describe silence. That was the time when I was sick ... and I was left alone in the house. The situation was so surreal ... because I even saw myself covering my ears. The tranquility was so eerie ... it was deafening because I could even hear my heartbeat ... and the house gecko making that guttural "squawk" was magnified ten times more ... enough to give me a good scare.
So oxymoron's words clash ... and if you just pause for a while and clear your thoughts ... the doubting Thomas in you will make your hands up and retreat at the end ... and become a new convert ... yes oxymoron's two words can be combined to make a phrase. Take these examples:
1. EXACT ESTIMATE - Estimate means you roughly CALCULATED ... it is an "EDUCATED GUESS". All you did was APPROXIMATE ... so how on earth could you possibly say ... it is EXACT? How could you possibly say it is CORRECT and ACCURATE in every detail ... when what you did is only SPECULATE and ESTIMATE?
Exact Estimate is an oxymoron.
2. FOUND MISSING - This is another oxymoron. Is this for real? How can you found something that is missing? If you are missing ... you are GONE ... you were LOST ... you were MISPLACED. You are nowhere to be found. Placing found next to missing seems incongruent.
The phrase "found missing" is correct and usable in written English. You can use this phrase to indicate that something has been absent ... missing ... or can't be found. For instance, "The championship trophy was found missing from the glass case in an empty hallway of the university's athletic building."
See English language can welcome all kinds of abnormality ... oddity and irregularity into its tent ... making it an anomaly if you start asking questions.