The Costco gloves are also good. And cheap. And you have to buy a whole-lot-o-gloves.
Try your local auto supply ie: NAPA
I gotta second the Harbor Freight gloves, they work for me.
Check with your dentist. We always get sample sizes of gloves in the mail. If you get them too small and use them repeatedly for long periods of time, developing trigger thumb is possible.
I've been using the nitrile gloves from Lab Safety Supply for many years now...also use some of the the heavier type gloves for general cleanup in the lab. check them out they have lots of good stuff for the darkroom
I use dish gloves, myself. But some find them cumbersome. I like that they are thicker, last for years, create less waste, come on and off easier when working, clean easier, dry easier when working, and cover onto the forearms, not just the wrists.
But you should be able to get the purple nitrile gloves (which I also have, for things other than darkroom use) from a tools catalog or your local independent hardware store.
If you are in a relatively rural area with cows try your local large animal veterinary clinic. They will usually offer very durable nitrile gloves for sale (meant to be worn while milking cows). If they don't have them I'm sure they could lead you to a source for them.