Local stores like Brafasco and Fastenal are good.
Lowes
I once walked into one of those stores (I think it was Brafasco) and they didn't have the nut I wanted in stock. The guy at the counter said because they had to special order it, I had to buy like 100 of them. I just wanted one...
So I went on eBay and ordered it. The nut (actually a packet of 4) arrived in an envelope, the delivery charge was the cost of a postage stamp.
+1. I deal with them weekly for work.Brafasco has a tight min buy policy lately.My favorite fastener store of late has been Bolts Plus.