I transformed a Surly front disk hub into a fixd hub using a tomicog and following these instructions...
http://www.fixedgeargallery.com/arti...mson/surlyhub/
It worked perfectly. With zero dish the Surly front hub yields a 45mm chainline. Of course, if you dish is slightly, you can move it either way a few mm.

If you have a 120 spaced frame with a "track" chainline (41-43mm), the best option would be to use a bmx disk freehub. There are few BMX disk hubs out there. I've spoken to the guys at Kore about this hub.

http://www.kore-usa.com/products/hub...r_disc_3x.html

You would have to put in a longer axle for a 120mm frame, but it will give you an approximately "track" chainline on both sides.