Nice to see some appreciation for this multi-talented, all-round musician.
I doubt whether a full list of his whistling contributions exists anywhere - it's probably just too extensive. I don't think even his website - http://www.alessandroni.com/ - is comprehensive.
My favourite of his whistling themes is probably Adios, Sabata; it's stayed with me ever since I first saw the film as a nipper.
As for his solo compositions, the only one I have at home that's relevant to Westerns is El Puro - that's well worth getting.
He also made telling contributions to gialli and horror films - The Devil's Nightmare is especially memorable, and there's a compilation of creepy pieces he wrote with Nora Orlandi called Music for Strange Situations that's patchy but frequently excellent.
I had the opportunity to interview him about 10 years ago prior to one of his performances in London, and he was a real gent.