Well, I wasn't going to answer seeing as I don't have any idea where to get a ready-made holster for your application. But, seeing as no one else does either apparently, I'll tell you what I wound up doing.
I have an Aimpoint on a Ruger MK II and couldn't find a holster for it either, so I took an El Cheapo Uncle Mike's nylon holster, cut a slot the width of the holster about half way down the front with an Xacto knife. The gun fits well, and the normal retention strap keeps it in place nicely. One of these days, I'll see about finishing the cut edge with some seam tape.
Not pretty, but cheap and effective.
I also have a Single Six with a Red Dot, and use a "bandolier" holster for it. Not something I'd like to carry around on my belt all day, but protects and retains the weapon nicely whilst bashing around on my ATV. Example from Midway here
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