I can't apologise enough. I must be going barmy!
You're right. It was Barium Nitrate I was thinking of. Barium Chloride, Barium Carbonate and Barium Chlorate would also be suitable.
Copper salts are usually combined with other inorganic salts to give a varying blue-green colour, but Barium is normally used to provide a true green.
I doubt very much that firework manufacturers would use pure elemental Barium for this purpose. Barium en masse is more expensive than its salts weight for weight and the pure metal readily oxidises in air forming Barium Oxide. The metal is usually stored beneath paraffin or other oil.
Barium salts would combine more readily with the inorganic oxidisers, fillers and other substances used in the fireworks.