There used to be a website from a universtity, I think in Ohio, that had a lot of information for people building their own units. Last time I looked I could not find it, so hopefully someone else will post a link. Otherwise there are the places like Accel (Mr. Gasket), FAST, Electromotive, etc. but you might already know about them. Most of their parts are just repackaged automotive standards that they can afford to buy in quantity.
Big suppliers like Delphi, Packard, and Bosch are almost impossible to get any help from.