Australian Sixpences were made from sterling silver from 1910 to 1945 and 50% silver from 1946 to 1963, never from copper although the later issues had a 40% copper content.
It would depend on your defintion of "bulk" but, yes, you should be able to buy them in quantity from a coin dealer if you can afford it.
If you are looking at recovering the silver, save yourself the time, effort and expense. It will probably cost you more to purchase the coins and recover the metals than you are likely to get from selling the coins intact to a collector or dealer.
Australian silver coins (5, 10, 20 and 50 cent) are composed of 75% copper and 25% nickel. There is no silver in any circulating Australian coin.
All British "silver" coins from 1947 onwards were made from a copper nickel alloy.
Silvery coloured Australian coins in general circulation are the 5, 10, 20 and 50 cent coins. Their composition is 75% copper and 25% nickel. There is no silver in any circulating Australian coin.
All New Zealand "silver" coins from 1933 to 1946 inclusive had a 50% silver content. All New Zealand "silver" coins from 1947 onwards, were made from a copper/nickel alloy.
An Australian Sixpence was a coin of silver appearance which was first minted in London in 1910 and last minted in Melbourne in 1963. From 1910 to 1945, their composition was 92.5% silver and 7.5% copper (sterling silver). They had a milled edge, weighed 2.83 grams and were 19 mm in diameter. From 1946 to 1963, their composition was 50% silver, 40% copper, 5% zinc and 5% nickel. They had a milled edge, weighed 2.83 grams and were 19 mm in diameter. All Australian coins have the reigning Monarch on the obverse, and the Sixpence had the Australian "Coat of Arms" on the reverse with the word SIXPENCE around the top and the year at the bottom. They were progressively withdrawn from circulation after the introduction of Decimal Currency on the 14th of February, 1966. In modern currency, a Sixpence was the equivalent of 5 cents. There were no Sixpences issued in 1913, 1915, 1929 to 1933, 1937, 1947 and 1949. The rarest Australian Sixpence is the 1918 coin and the 1922, 1924, 1939, 1952 and 1953 coins are considered to be scarce. From a coin collectors perspective, Australian Sixpences, depending on year, condition and method of minting, can be worth anything from $1 to $145,000 AUD. Please note that since the Sixpence is part of a redundant or obsolete currency, it no longer has an "exchange rate" with other currencies.
From 1967 onwards, no general circulation Australian coin has contained any silver, or any other precious metal at all. Since 1967, all Australian "silver" coins are made from a 75% copper and 25% nickel alloy.
The last British coins minted for general circulation containing any silver at all, were issued in 1946. These had a 50% silver content, the other 50% consisting of copper and nickel. These coins included the - Halfcrown (2 Shillings and Sixpence) Florin (2 Shillings) Shilling Sixpence The US stopped minting coins with silver content in 1965, though the dates on them were kept as 1964.
The British silver coinage was degraded from 1919/1920 from sterling silver to 50% silver. All British silver coins from 1919/1920 to 1946 inclusive had a 50% silver content. From 1947 onwards, all circulating British "silver" coins were made from a copper-nickel alloy.
Australian coins minted for general circulation in 1931 were -Halfpenny - 369,000Penny - 494,000Threepence - not mintedSixpence - not mintedShilling - 1,000,000Florin (Two Shillings) - 3,129,000The Threepence, Sixpence, Shilling and Florin were all made from 92.5% silver in those days.
The first Australian coins to be put into circulation were the Threepence, Sixpence, Shilling and Florin in 1910.
It was traditional to put silver coins into a Christmas pudding.
Copper has almost always been used in silver coins, because pure silver wears out faster.