If there is a farm and garden supply store near you like Tractor Supply, look for a product in the equine/cattle section called Permethrin-10. It's very concentrated permethrin. A quarter teaspoon in a gallon of water will make an effective mite spray.
DO NOT APPLY PERMETHRIN DIRECTLY TO YOUR SNAKE OR IN ITS WATER BOWL. Only spray it on the hide, paper substrate, enclosure, etc. and make sure everything is dry before returning your snake to its home.
For on-snake treatments folks have used Frontline very effectively.