Effect of a good's inputs on elasticity of supply
Consider the extreme case: all available quantity of the no-substitute input is already employed.  

To trace the supply function, let's assume that we are already at some price level, and let's increase the price of the final good: will quantity supplied increase? No, because it cannot do so -there is no available additional input to use for this increase. In this extreme case the price elasticity of supply of the final good is zero, due to the situation in the inputs market.

Assume now that a little quantity of the no-substitute input is still unemployed. Being unique, we expect that it will command a high price if it is demanded for employment. So increasing quantity supplied of the final good, bears a high cost in terms of steeply increasing production costs. In this case, the price elasticity of supply of the final good is not zero, but "small"...

...compared to the case where the inputs needed for production are generally available and so the cost to employ them is smaller than in the previous case. Here we expect that under the same as before final-good price increase, final-good suppliers will find it profitable to increase their quantity supplied more than in the former case -so here the price elasticity of supply of the final good will be "large"(er).