casting your own is an almost impossible feat. I have a bunch of silver ingots and thought I could AT LEAST just melt them down into a puddle, nope. I knew off the bat that the high temp would destroy my molds, but I don't even have a pot that can handle the heat. a cast iron pot would suffice, and you would need a steady source of heat, like acetylene torch or MAPP. as for a mold, not sure, you would need a nice silicone mold I suppose, or sand. lots of work.
if you have a lathe, and just melt some down into a decent size piece, machining would be fun.
or, just buy one of the types above, and hand-cut the top off, then grind the sides down to fit