Christer Bergstrom gives some good figures for the Battle of Britain.
About 40% of Bf 109s at the Channel airfields were E-1s. On 31st August, of 740 Bf 109s serviceable, the sub types were represented thus.
307 x E-1, 103 x E-3, 304 x E-4 and 27 x E-7.
E-1 production ended in August 1940, but of the 323 Bf 109s delivered to units on the Channel up to the end of September, exactly 100 were E-1s. I find it unlikely that new production E-1s were cannon armed, they would have been designated as a later sub-type at the factory.
We don't know how many E-1s were upgraded and cannon fitted in this period, but it usually happened after damage and a substantial repair.
The sub-type was far more common than most narratives imply. There is a general misconception that ALL Bf 109s involved in the BoB were cannon armed, and thereby more heavily armed than RAF fighters, whereas in fact very many were armed with four machine guns, just half the armament of the British fighters.
Cheers
Steve