I can't offer much in the way of source of the horns... but on the shipping, assuming things haven't changed all that much in the last 10 years... likely you will need to approach the dept of agriculture and obtain a Phytosanitary Certificate to ship out of the U.S.... into Spain will be another set of regulations that will need clarification by the reciprocal of the USA dept of Agriculture. I haven't ever shipped just the horns, but about 30 years back, I did ship a pair of horns that was still connected to the bull.... we had a breed bull fly out of San Francisco to Madrid... he showed up on a truck on one side of the truck, his cage on the other side... we set the cage on the dock and the handler backed him off the truck, pointed him to the cage and in he walked..... we had to have a veterinary health certificate for him plus import permits.
I've also shipped an aircraft container called an LD3 full of Hamburger meat, along with the buns for hamburgers... and another LD3 container of Coors beer... one of my clients to the Paris Air Show (back in the late 1970's) used the hamburgers and Coors almost like cash to get things done at the air show.... about the same time, we also were shipping Horse Meat to France... it's evidently a delicacy that the French like....
in all cases, I again had to have Photo-sanitary certificates for the food products, plus import permits.
Depending on what Tony needs, the trip out to a rancher/breeder/farmer/ etc locally might be the best solution....