I assume you mean the races are shot (and not the bearings, which should be easy to find). Whatever headset you choose, make sure that it has the right stack height for your fork. What type of headset do you have on their now? What about the rest of the components? A late 80s Shimano 105 headset would be a nice period-correct option if you require a low stack height.

I'm not very familiar with Cannondales, but I wonder if they require a larger diameter headset due to the over-sized tubes. To be honest, I get confused by the various inner/outer race & cup diameter measurements. You mention 30mm cups. FWIW, Velo Orange lists the Grand Cru crown race diameter at a standard 26.4mm and a (fairly high?) stack height of 42mm.