If I hear of one I will let you know. There are plenty of crossbreeders that do health testing. Just ignore people who bash crossbreeds. As somebody who works dogs I rely on crossbreeds 99% of the time because of the better health, longer lifespans and resistance to disease. My best hunter is a Labrador Retriever x English Springer Spaniel. They are known as Labradingers. Best duck and pheasant dog I've ever had.
A crossbreed is only as healthy as the genetics it is given. There is no sure thing that a mix breed is going to, by simple virtue of being a crossbreed, have better health or longer lifespan than a purebreed. Some will, some won't
If a dog inherits traits such as hip dysplasia, heart disease, eye disease etc, it inherits them regardless of the breed mix. Dominant and recessive traits can change the risk, but purely mixing breeds matters not when many traits are carried to some degree across many breed and/or if the individual dogs being bred for the mix have not been tested clear of the undesirable trait.
Like the others (most of them) have said, it is crazy difficult to find a responsible breeder doing the recommended testing on mixed breed dogs. Btw, most testing cannot be done until the dog is 2-3 years of age so any dog being bred should be at least that age.
Can someone carefully and ethically breed crossbreeds? Sure. To some degree this is done with working and sport dogs where proven athletic or work performance matters as much as pedigree. But for companion breeds, the temptation for a quick dollar is often too much and people know the market sells for cute designer dogs.