I think you know what you're asking for isn't common and tends to be a brief segment buried in other videos. There aren't a lot of women out there getting up in the morning thinking, why don't I do a video punching myself in the stomach for three minutes straight for the six guys out there who will buy it? So, there's no hidden trove you're missing. Your best bet is to go on herbicepscam.com, ask women if they'll do that, and get a private show. It's not something I specifically asked for, but a couple of women have done it. Unfortunately, no one currently active, but other guys here might be able to give you some names.
Ever hear of Jill Lauren? She's not a muscle woman, but her claim to fame is real abs punishment. Her vids are on darkflicks.com. Go on there and search for a video she did with bodybuilder Justine Delts. There's a preview. Kat Conners also has a video on there, but as I recall she didn't last long playing with Jill, so it's more about giving.
