The German site Spraydosen shop if searched for the words "avorio ruote Lancia" comes up with a colour that it says is right for Fulvia HF wheels- here is the link
http://www.spraydosen-shop.de/aerosol-spray-can-lancia-ruote-hf-avorio-ruote-fulvia-hf-uni-one-coat HF 1.3 wheels only were ivory, and contemporary with the series one Sport, so it might help. The product is a special one-coat paint, and I have not used it, but it might be good as a match. It must be worth trying to get it right!