Try calling around to some of your local junk/salvage yards (if you have any) and ask #1 - do they have any soft lead? or #2 - do they have any lead from scrapped out lead sheathed cable? I used to buy salvage lead from a local junk yard that was from lead sheathed cable - soft and worked well for casting. It can be a little dirty but that will be taken care of when you melt it down and flux it - I always use a small pellet of beeswax for flux and it works great. And yes . . . . I do all of my lead melting/casting in a well ventilated area.
If a pair of '51 Navies were good enough for Billy Hickok, then a single Navy on my right hip is good enough for me . . . besides . . . I'm probably only half as good as he was anyways. Hiram's Rangers Badge #63