Where is 蛮 used, as in the meaning of 'quite'?
As others have said, 蛮 is not exactly dialectal. Most Chinese speakers would understand what you mean if you use it to mean "quite."

However, it should be noted that it is colloquial--it shows up in spoken Chinese but rarely in print, hence your discovery of it on a Chinese TV show. In fact, some native Chinese speakers will confuse 蛮 with 满 when asked to write the word down.