Well then I just told you how, when you buy Great White or any other your buying spores, you wet, and feed them they multiplly... Or are you planning on finding those spores in the wild and identifying them and multiplying your own?
If you have ever worked with spores before, you could appreciate how much work could go into identifying and then multiplying what is in 1ml of forest soil. Even if you could identify them which would be the easy part, then isolating that strain and working it contamination free would be the hard part, great white has 15 different species of mycorrhizal fungi, 11 different species of beneficial bacteria and 2 species of trichoderm, chances are they dont even all exsist in your local forest soil. Without a Lab that undertaking would be near impossible, frustrating and a waste of time...thousands of hrs, growing out petri dishes which many would be contaminated.