MSC, McMaster, and Zoro/Grianger do sell them, but at $8+ bucks (and up) each they are a little expensive to incorporate into a product.
What's the secret source? (in the USA) I'd like to be able to order boxes of 100 or so of each likely size to keep on hand.
I did find some on eBay for a little less which I made an offer on for one idea I am working on, but I'd like to also be able to reorder as needed rather than search for overstock and salvage lots.