The only way in my Country (UK) would be through a prescription from your Doctor, that or finding a local drug dealer who maybe able to help. The first option is safe as you would get F, BUT they only give that stuff out to people seriously suffering hideous pain or dying, so its not something one could obtain. Second option is warranted with risks, often a dealer can get you what you want, for a price or so I'm told, but noone knows exactly what you are getting, very risky.
For what its worth I have used F patches on occassion when my physical pain goes through the roof and they are not very effective, you need oral and IV really to get results.