A quick search shows there are a little over 30M addresses with a nonzero balance, which is just under 2^25. That means the actual probability would be about 1

A quick search shows there are a little over 30M addresses with a nonzero balance, which is just under 2^25. That means the actual probability would be about 1/(2^135). At a million hashes per second, that means you would likely find one after about 10^27 years.