The easiest source in a tire shop. I've been able to get wheel weight metal for free so far.
You can make then quite hard if you want, by quenching them in water. You can make sofer bullets by slow cooling them, or taking the temper out of them in an oven.
You may find you want even softer bullets for the 44-40. That's where the fun begins.
Radiology and dentists offices use lead shielding in their walls, so watch for renovation projects there. Old houses used lead pipe for waste pipe. Usually the toilet pipe was lead, sometimes sinks, or bathtubs. Pure lead can be a ##### to get, at least free stuff.