Actually, I beleive 36mg is the strongest that you will find. You sound like you haven't actually found your riht nic level. I bounced all over the place for a couple months. Started at 24 and now I use 12 but, for quite some time after I got to 12, I would still vape a few drops of 24 in an atomizer for crave times.
It also sounds like you're trying to just quit smokes and only vape. That's not always the best way to get there and it's not how I did it. What I did was schedule three or four cigarettes a day. In between, I vaped all I wanted. When I had those cigarettes, I wasn't doing anything else. No sittlng at the computer, no watching TV, no visiting with anyone. I just smoked and noticed how it tasted and made me feel. After a few weeks, I found I really wasn't looking forward to those cigarettes. Then it was fairly easy to lay them down.