Diana Where can I buy balls cal. 4.40 No. 9 of Czech production?

Copper-plated 4.40mm balls that can be bought in the USA are not suitable. I have a can of balls made in the GDR and they are perfect for my Diana 30. I know that everyone uses copper-plated 4.40mm balls in Haenel rifles that can be bought in the USA and Canada, but for some reason Diana 30 rifles do not work with them.
John Groenewold sells 4.4 lead ball by the pound. Gaylord recommended it over the copper H&N BB because they may get stuck in barrel.
 
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