Vets and sand fly protection

Our boy has a Seresto collar, quite expensive but recommended by the rescue centre's Vet when we got him. He doesn't have Leishmania so we want to keep it that way.

Our two old dogs, both no longer with us, had Leish from their years of living outside when owned by a Spanish farmer. I tried them with Baltic Amber collars which are a natural (rather than chemical) way of repelling ticks. They worked well for that but I don't think I would trust them to repel sandflies.

Thanks. Do you get your Soresto collars in Spain or posted in from the UK? 

From our local vet here.