Because there are so many variations in stair locations, styles and materials, I don't think that you will find more than general plans for spiral stairs. I think that your best bet would be to check with the advertisers in the back of any of the woodworking or home improvement magazines. I have been in some shops that did produce these and the amount of gigs and fixtures that they had just for running handrails, for instance, was staggering.
If you do decide to try this on your own, please remember that there are building code issues to be considered. Some people think that these are "no big thing", but find out differently when they have to rebuild their house to sell it, or someone trips coming down the stairs and sues them. If you don't meet code, your insurance will not stand behind you. In my opinion, it's not worth the risk as a DIY project.