Can't speak for Corsas, but some years back it was common for underbonnet insulation to be provided only on the higher-specced models in the range. I would guess it is possible to get some from a dealer, or even off a scrap car if you're lucky, and fitting should be easy. I don't suppose dealers will give it away though.

I agree with Andrew. On Peugeots it was standard, then around 2007 they only added it to higher spec models.

I'm thinking further back than that, Gibbo - about 1990. I seem to remember some 205s had noise absorbent on turbo diesels? The 205s I have at the moment, both Garroses, were near the top of the range but neither has any bonnet insulation.