Old print type might be another, I think printing technology has moved on from that.
Maybe you know someone in a radiology lab?
By the way, it takes quite a set-up to melt and cast that size chunk of lead. Dangerous too. I would strongly recommend you think of some other way of doing what you are planning. G
If you know someone at a gun club, they salvage lead out of the bullet traps at the range. There was quite a barrel of the stuff at our indoor lanes.
Not the friendly guys in white coats and a weird thing for bondage I hope? Not again?