If you mean the strap part, you can buy them third party, and they're dirt cheap. Like $5 cheap. Can even upgrade to the HE1000/Susvara style, which is a bit nicer and I think more durable. Look on AliExpress.I mean Hifiman and in general not just you. I tried to get a replacement headband for my pre-Stealth Arya, I was told by Hifiman that they do not sell replacement headbands. Instead I bought some stuff to pad/protect the headband and hopefully it lasts forever and doesn't break.
Arya style, $4.50:
HE1000/Susvara style, $6-9: