There are so many crosses and unknown, never before cataloged pure landrace strains and so forth that yeah. If you want a viable number (since I'm pullin this outta nowhere): 1032 crosses and 28 landraces...just kidding...there is no real way to be know. if someone has a certain quantifiable number for you then there also pullin it outta there bum. Take care and Welcome to MP!
There's also some books called The Big Book of Buds Vol 1,2,3 By Ed Rosenthal I have all 3 and love them they don't have all the strains but they have all the strains from reputable Breeders! It deuails growing tips by the breeder of the strain as well as in depth look at Buzz,Flower Time,Yeild and the best method growing all from the breeders who actually bred the strains, it was a must have for me I leave all 3 on the coffee table and everyone can't put them down! Hope that helps you alittle