Hi red,
Long ago I would have tried using a hacksaw: get a hacksaw blade
with the biggest teeth possible, use wax for lubrication, hold the
bar in a solid vice and saw off slices about 1" thick. Arrange bits
of cardboard to direct the filings and lay newspaper around to catch
them. Then use a BIG sledge hammer and anvil to get the slices thin
enough for the rollers or shears. I also would have tried hammering a
hot set chisel (blacksmith’s tool) with my sledge hammer and chopping
off pieces.
If that sounds like consuming too much sweat and time, industrial
machine shops will be able to break up your bar one way or another
quickly and cheaply. Just be aware that they will contaminate the
filings with foreign metals, or embed foreign metals into your pieces
of silver, and take precautions to prevent that from happening.
Then again, you could simply trade your bar for granules at your
local pecious metals refinery!
Regards, Alastair