Hello, fellow Sunset Zone 17 gardener.
If I understand your request correctly, you're looking for drip trays (aka drainage trays) to go under the plant pots. You can purchase individual drip trays at the OSH on Ashby or the one here in El Cerrito. Maybe Berkeley Hardware on University carries them, but I'm not sure; it's been a long time since I visited them. Westbrae or Dwight Way Gardens might carry them; Berk. Hort. prob. thinks they're way too low-rent.
They come in several sizes, so you'll want to make a list of the diameters of the plant pots. Then purchase a drip tray approx. 1 to 1.5" wider than the pot.
I bought some of these three seasons ago, and they've been in direct sun along the south side of my house under my black plastic tomato containers ever since. No leaks yet!
Sunset Zone 17, USDA Zone 9