Hello there, I got a really beautifully finished stair runner/landing carpet made by M & L Carpets in Crouch End, who ordered in the specific triangular rods I was after and fitted the lot. They can do pretty much any carpet with a bound/contrasting edge, and were really very helpful. As far as I can tell they've been closed but not gone out of business. Good luck, here's their contact details: https://mandlcarpetscrouchend.co.uk/
Endorse M&L Carpets recommendation. Real craftspeople, taking pride in their work.