I don't get this. Not any more. I accept I can't stop the stutter, I can't stop the blocks. I just say what I need to say and hope that the other person can wait for me. I know that this can reflect poorly on me, especially when I'm speaking Japanese (I'm a native English speaker living in Japan) and when I block it can look like I don't know the word hence seem less fluent in the language. There's nothing I can do about it though. I don't think that there's any cure and am extremely sceptical of those who offer them, but as soon as you accept it you can work on slowly improving it. Acceptance is key.