I am a bit confused- I have literally tons of stainless polished every year, and I have never heard of the electropolish finish not being good enough. It is true that the finish will be a shinier version of whatever you give them- so if you give them a factory mill finish, it will be a shiny version of that, and if you hot texture the pipe first, it will be a shiny version of that.
What is the problem with shiny mill scale? It isnt coming off, it wont rust, and it looks a lot better than the unshiny kind.
If you want mechanical polishing, there is a place in the south end that has the machines- I did a bunch of work on the Baseball Stadium and I had the pipe I used on that mechanically polished. Cant remember the name of the place- but I think both Alaskan Copper and Seattle Boilerworks recommended them.
If you really want to do it yourself, you can get scotchbrite sanding belts for any belt sander, and go at it. Klingspor will make em to order to fit any size- I sometimes run em on my old Makita 1 1/8" x 21" belt sander.
Personally, I would order prepolished tube or pipe if thats what you want- it wont cost much more, and it will save an enormous amount of work. Alaskan should carry it.
Railmakers actually makes boat railings out of shiny stainless steel- thats their main business. They buy several sizes of tube, not pipe, prepolished and wrapped in plastic, by the bundle.