Scrapyards will have it. If you want really soft lead, ask for lead pipe. If you don't care, ask for wheelweights (much cheaper than lead pipe). They may have bullet range stuff there as well, mixed in with the wheelweights. Scrap yards are in business to make money, and right now lead is going for a fair amount.
If you can find a local range with a "Snail" trap (made by Savage Arms), ask if you can clean their traps once in a while. The bullets will be nice and clean, and you just shovel the stuff out. There may be some anti-freeze mixed in with it, so melt it the first time outdoors on a windy day if possible. Range lead tends to be a little on the soft side on the average. Jacketed bullets are pretty much pure lead (the jackets float to the top when you melt it and are easy to skim off). Cast or swaged lead bullets are harder. A mixture of the two is a somewhat soft alloy. It is probably too hard for muzzleloading rifles/handguns, but fine for cannon projectiles with adequate windage.
You could try e-mailing Savage Arms to see if they can point you in the direction of one of their bullet traps installed in your area.