Your question reminds me of a wonderful story from a therapist friend, who said he tells his clients who suffer from those harsh inner voices, "Man, if I were sitting in a restaurant, next to a table where somebody was castigating a companion with the same words and tone that's going on inside your head, I'd totally ask for another table."
You probably would too! So, good for you for setting your sites on silencing those mean voices.
We have a lot of good resources that would make a dent on those harsh internal messages, but I think the most targeted audio would be Traci Stein's excellent Healthy Self-Esteem hypnosis program. This is an extraordinarily well constructed, psychologically sophisticated, beautifully narrated guided imagery and self-hypnosis program, with three tracks that offer different approaches, each of them quite effective, but it's an extra bonus to have the variety.
You can find a full description on the page.
And Traci has ingeniously partnered this first-rate audio program with another one to play while falling asleep and during sleep, called (not very surprisingly) Self-Esteem during Sleep. This is especially good for people who may unknowingly be unconsciously resisting the positive messages they're hearing while awake (although repeated listening will usually override that tendency after a few weeks), and together, you've got a powerful one-two punch to counter that toxic self-criticism.
So I unequivocally suggest you give those two a try.
And if or when you're ready to add something new to this regimen, you may want to try something from another master of the craft, David Illig, who wrote and narrates another superb audio program called Increase Self-Esteem. Or there is also my positive Affirmations. But Traci offers so many tracks and such variety on her set, you may find you don't need to use anything else.
Good luck and let me know how it works out.