I think most hardware stores carry short pieces and most electrical suppliers around me have the long pieces. But I found this on amazon.

https://www.amazon.com/Legrand-Wiremold-CMK10-Cordmate-Cover/dp/B0015EA3P2/ref=mp_s_a_1_2_sspa?keywords=wiremold&qid=1686238439&sr=8-2-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExRjQ4M1ZIRk1VS0hCJmVuY3J5cHRlZElkPUEwNDY0MzgwMzZQMFJBTjJHWkY2RCZlbmNyeXB0ZWRBZElkPUEwMjc1MzQyMkdKSVc0REhUT0MyVyZ3aWRnZXROYW1lPXNwX3Bob25lX3NlYXJjaF9hdGYmYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl