Have a look here at AixiZ: www.aixiz.net one of their cheap modules that run on 3.2V may be what you need, or any laser with an AixiZ type module and the standard 3 element or single element lens could work, and you can add one of these to it: Circle lens kit for 12x30mm AixiZ modules, AixiZ I haven't tried one of these myself so I don't know but it looks to me like what your looking for. I and many others here buy stuff from them, they are one of our main sources of laser parts.
Teej, The 2 spots picked are out of the way for blade changes and sample manipulation. We don't need the full 360 deg image because of a plate that's usually on one side. My big concern is getting a 4" circle from the said spots since there's no adjustment of the image size.