Not sure if you know about this, https://github.com/seerge/g-helper
The following are all reliable
https://www.comms-express.com/categories/solid-core-cable/
https://www.kenable.co.uk/en/437-indoor-ethernet-reels
https://www.cablemonkey.co.uk/2683-bulk-network-cable
Not sure if you know about this, https://github.com/seerge/g-helper