I guessed what you want but "a luggage" is not english. A suitcase, a bag, a Valise a backpack, a duffel bag or a PIECE of luggage.
Why does this also translate to "I can't find..." in addition to "I don't find..."?
I would have translated this as I'm not finding a big suitcase, but I was afraid to get dinged, so I wrote the unnatural sounding "I don't find a big suitcase." LOL.
That's just how people usually say that they are unsuccessfully looking for something in English. You wouldn't say, for example, "I don't find my keys."
If you don't find a big luggage, maybe try looking for something that actually exists? Like, I dunno, a big piece of luggage? A large bag? The tooth fairy?
The tooth fairy doesn't exist either. Did you really think it did? Guess the course makers aren't the only imperfect ones around here. See what happens when you mock others? Hashem gives us a taste of the same medicine we give others, so we should always be mindful of the effects that our actions have on them.