Hi Fred,
just an idea: try out
www.jumble-goodies.de - it's a german shop which offers a lot of Cobra/Shelby goodies. On their web site they tell they have more than 250 race stickers in stock - maybe your horse shoes and the other one with the "S" are available there?
Otherwise I have a 1:10 scale decal sheet which also contains this pair of horse shoes with an orange point in the middle. Don't know if it's possible to enlarge it without quality loss?
Good luck!
gt40.freak