I used sand to make mine. It was pretty easy. I made a wooden weight first (didn't have much sucess with using a lead weight as a pattern) and stomped it into a sand box. The moulding process was very quick: stomp in a mould, pour the lead, wait a minute, hook it out, repeat. I've heard that using 'proper' moulds can be hard as the lead sticks in the mould and everything gets too hot to handle so each pour is quite an effort.
So, in answer to your question, no, I don't know where to get a mould
