I think that would be a worthwhile restoration project. If you post a pic of the head tube crack you’ll get some opinions from knowledgeable people on repair prospects. The paint and decals on the Supercorsa are pretty straightforward and shouldn’t be too exorbitant a cost, especially if you go powder coat.
https://www.wingedstore.com/spare-parts-85
You can get the buttons and seat clamp bolt directly from Columbus/Cinelli and avoid the exorbitant eBay markup. The shipping from Italy is a little pricy but the couple of times I’ve bought from them, I add in a t-shirt, bar plugs, etc to smooth out the cost. I would contact Cinelli directly to see about prospects of getting a fork; might be expensive but you never know! Otherwise I would just find a placeholder chrome fork and take a long view patient search for the right one.
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N = '96 Colnago C40, '04 Wilier Alpe D'Huez, '10 Colnago EPS, '85 Merckx Pro, '89 Merckx Century, '86 Tommasini Professional, '04 Teschner Aero FX Pro, '05 Alan Carbon Cross, '86 De Rosa Professional, '95 Gios Compact Pro, '95 Carrera Zeus, ‘81 Masi Gran Criterium, ‘81 Merckx Pro, ‘89 Cinelli Supercorsa, ‘83 Bianchi Specialissima, ‘VO Randonneur, Ritchey Breakaway Steel, Rivendell Rambouillet, Heron Randonneur, ‘92 Ciöcc Columbus EL