Loads of them on eBay, just measure the internal diameter and search for "fiat alloy wheel centre cap" ..... There's loads of different designs and colours often with the measurements in the advertisement
im looking for just one but there not cheap on ebay!. there seems to be a few types i have noticed, one cap is all round and the others have the spoke groove in them. yours look nice!
http://www.oyodomo.com/sc?p=OTk1NDk...YLFBq5f7tPgdznt7kjKSTt6ReAq7UHiRw=&t=1&ndom=2
http://www.ebay.co.uk/itm/NEW-Genuine-Fiat-Stilo-17-Claw-Alloy-Wheel-Trim-Hub-Centre-Cap-50900835-/380695709968?pt=UK_Cars_Parts_Vehicles_Wheels_tyre_Trims_Trims_ET&hash=item58a33b8910
http://www.ebay.co.uk/itm/FIAT-LANC...heels_tyre_Trims_Trims_ET&hash=item3cd4b0de1d