[padobson]

Centralized? Not any that I know of.

Secretaries of State seems to keep shapefiles of their districts, but its never all of them. Check those websites first.

Local boards of elections are required to keep some record of the precinct maps on hand, but in many places aren't required to keep past ones - so it is in fact impossible to keep historical GIS data for some counties. There's also a lot of cases where records are simply kept as pencil or pen sketches, and no shapefiles exist.

You want to build a majorly disruptive business? Provide brain-dead-simple GIS tools to boards of elections so they can re-draw their own district maps every year. Offer them to software for free, and then resell the data they create to people building campaign tools - or build your own campaign tools and sell those.