The Kings below Pine Flat is class 2, runs all summer in most years and is close enough for after work boating. The San Joaquin below Friant is mostly flat water and usually low water at that. There is a tiny bit of play boat potential in Friant and just downstream in Lost Lake Park. Mystery Hole is on a nearby ditch and is really good, but not as deep as you would like for throwing ends. It should flow all summer and into the fall.
The Kings upstream of Pine Flat reservoir is still flowing and is a very nice class 3 run. Harder runs upstream. Lots of options in the spring and early summer. Kaweah, Merced, NF Kings, Dinkey Creek, Sections of the San Joaquin.
It does not seem like there are a lot of whitewater kayakers in Fresno, but they may just be hiding. Ran into a fellow last year who came to Fresno for work. He did not have a kayak, but had worked as a video boater and guide on the Zambezi. There is a small but really nice outdoor adventuring community in Fresno. People tend to do a variety of activities depending on the season. Many boaters in the area are also rock climbers and canyoneers. The Fresno area has some of the best canyoneering around, so it is easy to get wet in a river canyon after the whitewater has dropped off.