I understand your frustration.
Naltrexone is used for alcohol and other addictions. It is generally dosed at 50mg 4x daily. In that dose it works as an opioid antagonist. It seems ironic that in small doses it may block pain, which is what opioids do. It is a prescription drug.
LDN stands for low dose Naltrexone, the same drug used in very small doses. There have been some studies claiming that LDN can relieve some of the pain of peripheral neuropathy (PN).
In order to obtain LDN, one usually has to go to a compounding pharmacy, who will make it specially for you. This is expensive and inconvenient.
I tried it myself. I used 2 50 mg tablets, crushed them and dissolved them in 100 cc of water, making a solution of 100mg to 100 cc of water, or 1mg to 1 cc. I purchased a pipette (cheap, and reasonable if it works and you'll use it for a long time), and drew up 4.5 cc (4.5 mg) and squirted it into a glass of water, which I drank daily. It didn't work for me.
My pain doc told me that sometimes less or more will work. I didn't bother with trying different dosages.
Hope it works fo you.