I'm sure there are others, but all of these had one or more kinds of lead shot in stock when I checked just now. You'll pay around $40-50 per 25lb sack of shot. Buying multiple sacks might be wise, to combine the shipping. Maybe check multiple sites to see who gives the best delivered price.
I would go to a local trap/skeet club. the club I go to has lots of shot, primers, 209's plus rifle and handgun. And a good supply of powder. the club I go to has the best prices in town.
You need to go in person to where ever you find any shot. The shipping will kill you for just a bag or two. Right now I have found that it is cheaper to just go to the Walmart and get those 100 round boxes of dove loads.
If you are the handyman type, you might check out that shotmaking device I have seen advertised in the past. That and a bucket of wheelweights should get you going. Use good ventilation when you do this though.
I haven't gotten low enough to buy it online yet, I try to get in touch with local trap shooters going to a big shoot and usually there is a distributor or two selling it. I've picked up plenty from local stores.
I make my own shot as well. It's quite an operation.
