You may want to try roller burnishing the ID. You will have to do it from both ends as the standard tools are too short to go through in a single pass.

http://cogsdill.com/pdf/USCatalogs/Cogsdill-SR-Ser...

• http://cogsdill.com/pdf/USCatalogs/Cogsdill-SR-Series-Roller-Burnishing-Too

Ecoroll is another provider of roller burnishing tools, and has long products optimized for hydraulic cylinder bores, etc.

http://www.ecoroll.de/en/products/processing-cylin...

I know that they are not local to you but try these guys
http://elkhornelectropolish.com/
They have done EP on 0.250" x 0.035" tube for me.

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Plymouth Tube

If you can't find electro polishing services to that size, some other thoughts:
1. Flex-hone makes a 6mm brush-type hone. Google the term 'Flex hone' or 'brush hone' - they have various grit sizes.
2. We used to use a process called 'flow honing' for small diameter bores in the rocket biz, google the term for more info.

The real catch here is what type of surface do you want?
All of the suggested methods can reach smooth surfaces, but you working with surfaces that are smoother than a profilometer can work. It may give you a reading but it is meaningless.
Do you want a special surface texture? Do you know for a fact which texture is better for you application?

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Plymouth Tube

Thank you all for your replies, the roller burnishing suggestion is of great interest and we will investigate further.
Some additional info regarding our requirement: The reason we need a smooth surface is to prevent electro-static charging within the
SEM Electron Source that this component is used in. A honed finish will traps minute particles that can charge up and cause problems
to the image. So it's more about surface symmetry and cleanliness than an actual surface finish value, hence the small Rt value (not Ra).
If we could electropolish consistently along the length of the bore is would provide the perfect finish but maybe this is not possible?
Roller Burnishing could well be the answer. but we are also investigating Abrasive Flow Machining.....

It seems electro-polishing is particularly appropriate for you because it operates on the same principle you are working to prevent; electric emission from high points. To electro-polish a long bore you would need to use a wire or rod in the center of the bore. This is a complication but not an insurmountable barrier.

They use a wire with glass or teflon beads strung on it to keep it centered.
At this length they probably won't try to do it all at once, but rather slowly draw the active section of the electrode up through the part.
It is a pain but guys do it all of the time.

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Plymouth Tube