Now more than ever you really need to cast your own, just think about it, you will have an endless suppy at all times, you can make them the hardness you desire, depending on the velocity you have in mind, you can make them any diameter you choose (very important) & it doesn't take a lot to get started.
Here's what I did back in the sixties while in the military. I used a 4lb Lyman pot on the kitchen stove, casting with a single cavity #358429 mould, sized them in a used Lyman sizer & shot a semi load of Texas squirrels, frogs, turtles, armidillos, possums, coons & snakes, and a whole lot of dirt clods in between. Having to pay the high cost of good cast slugs & shipping on top does't save a lot over jacketed. You can scrounge range lead for mid range loads, lead, linotype & wheelweights are still out there if you're willing do get off the couch & do a little looking, times wasting, a year or two from now you might be very sorry you didn't get started. Things are changing fast, if you want quality cast slugs at a cheap price make your own. I've struck out at a lot of garage sales but I"ve hit a bunch of home runs too! Don't see any casting equipment.....ASK!