HD sublimation aluminum

[Boyan]

Hi, i am looking to buy from the 1mm white gloss and brushed aluminum gloss, best quality aluminum and i am very surprised to find that its available in all sizes but not the correct ones. meaning slightly smaller than A4 and A3 . I need it for outdoor signs. The idea is maximum value from minimum printer A3, but all providers think otherwise it seems. I don't know from where they have invented their strange sizes??? We have A4 and A3 printers. And eventually half of A4 and A3 for panorama photos.

Any idea from where to?

And while i am here, any idea from where to buy A3 size roll sublimation paper? I would like to make my Epson 1500W work with roll paper. As i need 50cm prints.

Thanks!