I have a guy up in NH who can cut it for you and also do any sort of custom cutting you'd like.
I've had 3 guns done by him so far. You can PM me if interested.
You can tell him what you'd like to do and he'll send you a 3D PDF of it before he starts.
Keeping it local and personal. You drop the slide off to him in person and he'll get to in a week or so. Nice guy too.\
You are on your own with finishing though. I'm still working through finding the best finish (see my other thread in this forum)
This one was simple. He angle cut the top edge of the slide from the rear of the ejection port forward to the muzzle.
He also cut the optic for the Shield/Holosun fitment.
But I have had him do window cuts and serrations on another gun.
View attachment 408476