Me and my Brother have used this company in the past for panels. Including sills for various cars.
https://www.carz2.co.uk/fiat-16234-c.asp
They haven't got the Stilo listed on there website, but it could be still worth a try as they will also post via courier. Assuming that they are still open with the current situation.
There also these listed on ebay via Poland.
https://www.ebay.co.uk/itm/FIAT-STI...:Stilo&hash=item3fd88f0164:g:ZggAAOSwh0BeJboE
Although they are more tailored for the 5dr at the rear and are likely just cover sills. But they could still provide most of the right profile for the front sections, if you could get them patched.
Only other thing you could perhaps try is a Blacksmiths if there one local, maybe they could fabricate some repair panels?