Your best bet for that type of boar might be rattlerow farms nr Stradbroke. They specialise in more modern breeds and I've been told that they will sell their 'used' 2 yr old boars to bring new bloodlines in.
Our vet mentioned them to me when we started out. He thought their hygiene standards to be high and so if you brought a boar in, the disease risk would be minimal (and fertility proven).