I found this on the Sennheiser website (which is not that easy to navigate) as an accessory for HD580:
“Replacement Cable with PX-4G adapter"
Code: H-55610/PX-4G
Price: $16.80
The URL is
http://sennheis.4ecommerce.com/mivastore/merchant.mv?Screen=CTGY&Store_Code=Refurbished&Category_Code=H39
or, if that does not work, start at
www.sennheiserusa.com
“Replacement Cable with PX-4G adapter"
Code: H-55610/PX-4G
Price: $16.80
The URL is
http://sennheis.4ecommerce.com/mivastore/merchant.mv?Screen=CTGY&Store_Code=Refurbished&Category_Code=H39
or, if that does not work, start at
www.sennheiserusa.com