The answer to this question really depends on what you consider "Mirror polished".
Mirror polished can be done to different levels. I've seen mirror polished mean anything from "I can see my reflection pretty good in the side of the blade, but there are a lot of light scratches that I can see"....to...."I could do neurosurgery in the reflection in this bad boy".
You can get a so, so mirror with just really high grit sandpaper....say upto 5,000 grit. That provides a pretty darn nice mirror. But, 8,000 grit sandpaper and some pink compound on a buffer will make it even more so.
The problem with using a Dremel, as RRLOVER eludes to, is that the drum is tiny and you'll never be able to even it out with that tiny thing. You need a large buffing wheel. However, such a wheel will heat up the blade quick fast and you can damage the blade with a buffer if you're not careful.