From a German website to be honest (
http://www.messerschmitt-bf109.de/ ) the author based his knowledge on a book about the Me 109 written by Rodeike/Prien. Maybe the number is too high - who know's, i also found some numbers around 200 at another page, but at least that would fit with the fact of only one company converting these planes.....
I have some more book's available regarding this plane, in case i should find some more information, i will let you know !
Thomas