I have looked into the same..it seems that all there is out there is campus style schools (the kind you have to go to and stay at) Ive come to think though that as with most trades a good reputation and great service would far outweigh any diploma. I just decided to buy a cruiser, stripped it down and add improvements to it, along the way learning how these components work in relation to one another, and picking up a few used and re-building those the same way, sell them at a fair price with a guarantee, and just let people know Ill do basic repairs for the price of the part and cost of any special tool needed or a few bucks.
Cheers
Chainmaker
Also the bicycle tutor site is a must