It can be sourced in the UK but the person(s) concerned must be on the GMC register and obtain a separate license from the Home Office for prescribing it as treatment for addiction. Even then there are strict limits each individual can prescribe and the quota can only be raised in the case where no other suitably qualified practitioner can take on the person so to get it in any amount worth selling it incredibly difficult and it comes in 150ml solutions in the UK and can be made as a crystal on request to the pharmacist assuming you have the proper authorisation from the medical practitioner, but yes all such medical purities must be 99.95% or greater unless it would be infeasible to do so for whatever reason.