Hessayon in the ‘Fruit Expert’ reccommends a mixture of carbendazim & fenitrothion spray for blossom wilt and mildew in Apple trees. Where would fairly large amounts be obtained. Enough for 60 trees, Fiesta and Jupiter
In any case, fenitrothion is an insecticide while the two problems you mention, namely blossom wilt and mildew are both fungal diseases.
Blossom wilt is not so amenable to control and the only thing can be done is to remove mummified fruit and prune out withered shoots. Apply some potash and do not feed with manure or compost.
Products containing myclobutanil are effective against powdery mildew, and apple scab, such as Doff’s Systemic Fungus Control or in large volumes, Systhane.
Try National Agrochemical Distributors in Dublin for the latter.