You can start with Nigel Saunders
Nigel Saunders if you want a course in 'Playing with Plants' in stead of seriously doing bonsai, and if you believe Aloe vera, Yucca and pencil cactus are good for bonsai. OK, he probably has some good videos but you'll have to be very selective.
Graham Potter
Great videos, but do understand that the bonsai he creates by carving massive trees are maybe shaped in a short time, but required a very, very long preparation. Do not expect you'll be able to do the same thing without years of practice.
Ryan Neil
Very good indeed. Some of his videos probably a bit much for beginners.
The course on this site is pretty good, imho.