There are a few options you could choose from. Gnonon does have some classes for that. i would also look at CDA http://conceptdesignacad.co/if you are local to the LA area. CG Master Academy (CGMA) could be another option for online. We have a full environment design program that includes Matte Painting, Environment sketching , environment design, etc. You could follow the track or pick and choose any classes that you want in any order. Good luck with your search.