Do you have the actual 2206TGT, or just a 2206 with the target adjustable rear sight?
I have a red dot on a rail mounted to the existing drilled and tapped holes on the muzzle of my 2206TGT. The rail is a Weaver 407S available on eBay.
I also milled a slide and made my own mount for a red dot on the slide, currently on my test 422. There was concern about the additional weight, it cycles fine, I took a lot of metal off of the slide to help compensate for the additional weight. I don't have a pic of the gun assembled, but here is a pic of the slide. I cut down a weaver 407s for the mount, drilled and tapped to the slide.
Here is a pic I have from someone that used a dovetail mount on a 2213, no idea what the mount is.