Yup, mine were pretty much guaranteed to be copper before 1984, say 1980 for safe. But recently the whole canadian shift toward the no more pennies solution, since it cost more to produce them than what they are worth.
Pretty sure US or UK have pure commercial grade, just need to know the year before they start using alloy.

Alternatively, those copper pipe from the hardware store could work, all copper pipe must be above 99.9% according to the copper developpment and association.
http://www.copper.org/applications/p...pipe_stds.html