If you have a Lowes & Home Depot both nearby, check them both. For some of my fancier PVC work I find I need pieces from both places that the other doesn't carry.
Besides that, see if you have a real plumbing supply warehouse in your area. They tend to not be the most user friendly places 'cause they're geared towards professional business only, but the one near me has the most comprehensive selection. You'll probably have to look them up in the yellow pages though. It won't be next to a Walmart, it's gonna be buried in the back-lot of some industrial office complex in the blue-collar section of town.
"Do, then talk about it.
No do? No talk!!" - Tom Barr