You need to look at more than the THC%. The interaction and ratio of other cannabinoids (like cbd) in relation to THC and each other is where the medical value is.
eg: there would be a drastic difference between the following two plants. Plant one has 15%thc 0.01% cbd would feel a world of a difference to 15%THC 6%CBD. And thats just the two cannabinoids. There are people that get more relief from lower thc and higher cbd. People that dont know much about cannabis and are trying to find whats right for them can be lead down the wrong road if we start thinking of THC as a % where the higher is better. Higher THC doesnt always mean its going to be better for your medical needs. And higher THC is not a measure of quality neither. Its a very general and monolithic way of looking at cannabis. So many different highs, and pain relief and sensations can be felt by not just focusing on thc. If I wanted a soaring up high I would be focusing on THCV more than THC. You know what Im saying?
But to answer your question a designated grower or you can grow whatever you want to grow. Under the current system you can grow it yourself. (technically you need to buy HC seeds but its not enforced) Under the new MMPR you will have more choice since they will allow any seeds officially and the freedome to experiment with breeding and further research into many different varieties.