Where do ear mites come from

I don't know that I have ever heard. They may be out there everywhere like fleas, or maybe a dog has to catch them from another dog. I haven't see a case in years. I think some the flea and heartworm remedies kill them too.

where do ear mites come from
They catch them from other infected dogs, I thought

Ear mites are extremely contagious. They can be passed from the mother animal to her offspring. Additionally, the mites are easily spread to other pets within the household including cats, dogs, rabbits, hamsters, gerbils, mice, ferrets, etc. Humans are not affected.
It is often recommended that all animals in the household be treated at the same time.