Is 'bir' actually necessary here?
If you use an adjective with a general direct object, include "bir" is required
"Bir kırmızı kanepe almak istiyorum" is not correct? Why can't bir be before kirmizi?
It just isn't how Turkish works. "bir" goes between the adjective and the noun. If you put it in the front, it is really stressing "one" as opposed to "two" or "three" :)
But English might just indicate that by a stress accent on "a."