need help with costumes!

[jvrjenivs]

Also, as far as I know, the leather arm bands is a hollywoodism.

Partly it is. Some sources depict 'arm bands' but these are probably just leather straps wrapped around the arm. As I saw in my re-enactment activities, I always need some more leather straps to fix one for my helmet, armour, etc. it also support your wrist, when wrapped cerfully. I would say leather arm bands are wrong for legionairies. Use leather straps wrapped around your arm.