Considering recreating impression of Obergruppenführer John Smith from "The Man in the High Castle " for Halloween or cosplay party? 

The armband of the American SS available here is sold open, so you can adjust it to the size of your arm. The total length of the armband is ~25inch (63cm) which should be enough even for Arnold Schwarzenegger (22inch biceps).

Historically SS armbands would be sewn to the uniform, but you may also just slide it on after adjusting the lenght to your need.

Note: Armband have 3 sets of snap buttons but my supplier  placed them too far for any practical use. I recommend simply ignoring them - for vast majority of sizes, they will be beyond what you'll cut off anyway.