@GimmickNG, "Le chapeau est disponible en noir." That's the "translation" I came up with as well. but as you probably know, that means it's 'available' in black. (which would also mean that it has to 'exists'). I'm wondering why 'existe' was chosen if it's not an idiom. (It doesn't make much sense to me).
"The hat comes in black" or "...is available..." would be a more everyday used english translation... Not many people would say the sentence above.. although I can imagine a slightly sinister shopkeep stroking his ample moustache saying "why yes, the hat does exist in black"
Yes - I live in France and if I am in a clothes shop and want to know if a dress comes in a another colour I would ask 'Existe-elle en noir?' or fr a dvd 'Existe-il avec les sous titres en anglais?' I am not fluent, but I use and hear this constructure all the time. Hope this helps - though I am a little late in the response, haven't been on here for ages.
It is an usual French sentence, which only means is available
cette voiture existe en blanc= this car is available in white
ces chaussures existent en différentes tailles= these shoes are available in different sizes
We have the same problem with the skills French>>English, with idiomatic sentences translated word by word and the result is stupid or abstruse.
My advice is this: Try to watch the discussions closely. There are native speakers willing to answer if a sentence is in correct French or not. Just don't give up hope and always report if you find a bad English translation (after checking in the discussion section if it is maybe just a strange sentence but correctly translated). And have fun! :)