These companies produce metallic alloy targets for sputtering machine. Their dimensions are much larger than what you need. But you can contact them, they may make the dimensions that you need.

https://www.sputtertargets.net/sputtering-target-materials.html?source_campaign=&gclid=EAIaIQobChMIpJaLz7Tl2wIVibXACh3sjQGmEAAYAyAAEgJxsfD_BwE

http://www.sinomaterial.com/e_products/?big_id=8&gclid=EAIaIQobChMIpJaLz7Tl2wIVibXACh3sjQGmEAAYASAAEgJkLPD_BwE

http://moltun.com/products1/solar-sputtering-targets/?gclid=EAIaIQobChMIpJaLz7Tl2wIVibXACh3sjQGmEAAYAiAAEgLObfD_BwE

https://www.angstromsciences.com/

https://www.enfsolar.com/directory/material/sputtering_target

Maybe it is avalaible in Goodfellow or Alpha products.

Best regards,

Pedro