If you are in a hurry and don't mind getting ripped off, Winsupply (Winwater / Winnelson) are great. They have the things big box stores don't carry. BUT...at a steep markup!
If you can wait a day or two, find a good plumbing supply that will let you shop online without an account, or check some of the farm supply stores (unfortunately not the ones you can just drive to in Castle Rock). You'll save 20% - 40%
I mistakenly thought pros got a much better deal at Winsupply. Nope, they still pay a lot more -- even with their volume -- than I can get the exact same brand product from my go-to plumbing supply. The pros just don't care if they are paying more, because they will just be passing that cost along to their customers.
So yea, if you're over a barrel this is the place. Otherwise not. read more