This is the time where most native mantis starting to develope into adult where mating pair can be located. Go on a hot sunny day with eagle sharp eyes. Watch out for sun burn
!! After October they will tend to be less as most have either die of old age or not active due to cooler weather.
Mantid season is in full effect here where I live. One thing you can do is set up a bright fog light in your back yard and males will usually be attracted to it. Females tend to be more sedentary and stay put, so you'll have to go out and search for them. Rick and other have suggested looking in overgrown grassy areas where there is little human activity.
I just found one outside earlier! It's a male stagmomantis californica. He's probably two molts away from adult. What's great is that I found a female a month ago.
Late summer, about nowish, is best for places with cold winters; they die in the winter and hatch in the spring, so it takes until this time of year for them to become large adults which are easily seen.