Looks like K and S rocketry is selling their remaining tubing on eBay.
https://www.ebay.com/itm/LOC-tubing-and-more-/272281751468?hash=item3f6541cfac:g:8mMAAOSwbYZXacb6
https://www.ebay.com/itm/LOC-tubing-and-more-/272281751468?hash=item3f6541cfac:g:8mMAAOSwbYZXacb6