I don't imagine any of the holster manufacturers ever imagined anyone would want to carry a 5" M&P IWB. (I'm getting strange pictures in my mind trying to imagine that... "is that a pistol you're carrying, or are you happy to see me"
). All kidding aside, you might try contacting Blade Tech, they've made some one off holsters for people I know and might be able to help you.
OOPs, forgot...Welcome to the forum, first post and you get a smartass response.