If the Tipo really is largely made from existing Fiat components, then I would not be surprised if there is a direct replacement from ,say. 500x. But I can't find any compatibility info. (or comparative dimensions) on the net.
I have kept a broken spring from a previous break so that I can start hunting spring pairs of similar dimensions. I have had 3 break so far. The point of break always the last twist of the coil at the bottom. Have run for 3 months with a broken spring with care but no obvious handling compromises.Fiat dealers always report back order. The only after market parts are lowering springs which I dont want. There are very few Tipos in breaker yards. But I still have faith in my Tipo which is still going strong at 96k