Try Reptile Relief.
You should have been able to find several mite killers at local pet stores or let a pet store order it for you.
ZooMed has a product called Mite Off. I had a problem with mites for the first time this year. I had switched a coulpe of my bigger snakes to cypress mulch as a substrate and it wasn't long before I noticed mites. I switched back to using news paper as a substrate and used Mite Off to get rid of the mites.
I recently made an order with Reptile Basics that included a 16.9 oz. spray bottle of Reptile Releif in case I have any more mites show up.