Dispersed camping is not permitted anywhere in the San Gorgonio wilderness.
The best map of the area is probably a matter of opinion, but I carried the Tom Harrison map of the wilderness with me for years and found it very helpful. You can get one on amazon, from the SGWA store, and it’s usually in stock at REI.
Check the trails link on this website for more info on where to find the camping conditions you’re interested in, and the wilderness permits link for info on how to get permits to camp at the specific locations where camping is permitted in the San Gorgonio wilderness. Enjoy! Beautiful up there this time of year.