Doubtful, but irrelevant.
"There are 41,500 Diocesan and Religious priests in the United States today. During the past 60 years 25,000 priests have left the priesthood in the United States and over 120,000 priests worldwide have left."
but how many went to become Protestant clergy. Most Catholics who left the priesthood still stay Catholic, just laicized. The ones who do go to Protestantism as clergy tend to go to the mainline-liberal ones such as Episcopalians, ECLA Lutherans, and Methodist, etc.
I meant as a percentage of clerics going to serve in another faith. In many cases the more devout are discouraged from pursuing vocations...Agony in Albany, etc. I have heard similar things from people in Boston.