According to Alfred Price in his book, Spitfire- A Complete Fighting History, "up to September 3rd 1939 the RAF had excepted delivery of a total of 306 Spitfires,of which 187 formed the full equipment of ten squadrons(Nos 19, 41, 54, 65, 66, 72, 74, 602, 603 and 611) and part of the equipment of one more(No 609)"
Hope this is of some help.
Bill