The bullion market has coins and rounds and bars from literally all over the world. If you just want to invest in, or stack up, silver there are many options. Those “trade units”, though, are pieces of history.
I wouldn’t mind having one if the markup isn’t too much.
I mostly have American Eagles but I do have some private rounds. Also some 5 oz bars.
Would like to get one of some other countries if the markup isn’t too high. Got a 2oz Canadian silver for less than the US Eagles would have cost me.