Tin ingots or Lead/Tin solder on not cheap but available, you can use old Type Set letters they contain Lead / Tin and Antimony both will harden Lead, getting hard to find these days, be careful Antimony will make very hard if to much added, lots of mix ratios on the net.
If you get a chance and your range will let you retrieve some old bullets, probably at the right hardness, melt and recast, best and cheapest if you can get permission, if just starting casting one word of caution make sure everything you melt is bone DRY 1 rain drop size drop of water in the melting pan will explode in a spectacular manor and it's Bl**dy hot. hope this helps