If you want to grow high quality Cannabis, you first need to get good seeds typically from an online seed bank or a reputable Cannabis dispensary.
Typically though, there will be a much better variety of strains if you choose to look at online seed banks.
You can find virtually any strain for sale, though it is true that some strains are harder to find than others. Some strains are so popular that you will see that these strains are commonly sold out. You can get either regular seeds, or seeds that are feminized. Most people prefer to go with feminized seeds because the females are the plants that create the buds. If you know about Cannabis, it is the bud that you are looking for as this is the medicine of the plant. The male plants will only produce pollen. If you wish to produce more seeds, you might want to just get regular Cannabis seeds, but this way you won’t know how many females you will get compared to males. With feminized seeds, you are guaranteed all female plants and you don’t have to worry about killing the male plants. You can also learn how to clone which is an essential skill to learn as a Cannabis grower. When you learn to clone, you can effectively make as many plants from a single plant as you want. If you know how to clone, you never will have to buy that strain again if you keep it alive through the cloning process. And with plants that are never pollinated, you have what is called sensimilla which produces no seeds and has the highest quality cannabis buds.